• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/105

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

105 Cards in this Set

  • Front
  • Back
Why is the facial nerve important in the horse?
The nerve is prone to traumatic, neoplastic, or inflammatory processes, producing facial paralysis. Trauma is common and the signs are dependent upon where the lesion is located. It can be damaged due to improper padding of the horse's face during anesthesia.
How can the horse's lower lip be anesthetized?
The mental nerve can be blocked at the mental foramen. The nerve is easily palpated against the mandible.

To desensitize the canine and incisor teeth, the deposit has to be made 3-5 cm within the mental foramen.
How can the horse's upper lip and nose be anesthetized?
The infraorbital nerve can be blocked at the infraorbital foramen. The nerve is palpable.

Injecting 2.5 cm within the foramen will also desensitize the deep structures of the face to the level of the medial eye angle, the first two upper cheek teeth, and the canine and incisor teeth.
Which vein can be used for "facial vein venipuncture?" How is this performed?
The transverse facial vein can be "hit" at 90 degrees to the surface of the masseter m. one finger breadth ventral to the facial crest even with the medial canthus of the eye.
Which nerve can be blocked to eliminate blinking? (hint: superficially nerve on the face)
The palpebral br. of the auriculopalpebral nerve can be blocked as crosses the highest point of the zygomatic arch.
Which lymph nodes are commonly abscessed in strangles?
The retropharyngeal lymph nodes, in general.
How can the guttural pouches be involved with respiratory infections?
The pouches communicate with the nasopharynx or can be invaded by diseased retropharyngeal lymph nodes - which lie against the wall of the pouches.
Accumulation of pus and exudate can cause the pouches to swell.
Also, blood vessels lie against the roof of the pouches and can be affected by Mycotic infections.
What is dorsal displacement of the soft palate?
The caudal edge of the soft palate rests on the epiglottis rather than laying ventral to it.

Also, epiglottic entrapment can occur where the epiglottis is permanently covered by the mucous membrane on the rostral surface of the epiglottis.
What can can diseased paranasal sinuses?
The overlying bone of the sinus(es) can be kicked and fractured --> this usually leads to infection.

Also, the upper cheek teeth that project into the sinuses can be diseased.
What is laryngeal hemiplegia (roaring)?
It is produced by partial paralysis of the intrinsic muscles of the laynx (especially the cricoarytenoideus dorsalis). The paralysis allows the vocal fold to swing into the air current. The ventricle fills with air and a stenosis of the laryngeal lumen occurs.

Usually all of this is caused by damage to the recurrent laryngeal n.

Treatment:
The larynx can be entered by a longitudinal incision through the cricothyroid ligament. The ventricle is everted and cut off. Thus, there is lateral adhesion of the vocal fold, preventing it from swinging into the lumen of the glottis.
Also, the cricoarytenoideus dorsalis m. can be simulated by permanent suture of the muscular processes and cricoid lamina towards one another. This causes the vocal process of the arytenoid and the vocal fold to be abducted.
List three superficial structures/characteristics of the equine head.
Skin is thinner along face than elsewhere on body. (Vessels are easier to see/palpate/be damaged.)

Tactile hairs are numerous along lips, chip, and margins of nostrils. (Very sensitive)

Many areas of face are not covered extensively with soft tissue structures, including dorsal aspect of nose, forehead, part of temple, and most of mandible. (Palpate vessels that cross these locations)
Describe the equine lips (Function, characteristics).
Lips are motile and sensitive—used in selection and prehension of food; allows for effect of twitching.
Describe the oral cavity and its components.
Oral cavity = oral cavity proper + vestibule

Oral cavity proper = bounded dorsally by hard palate, laterally and rostrally by dental arcades, ventrally by tongue, caudally by palatoglossal arch.

Vestibule = lateral portion of the mouth, lateral to teeth arcades; communicates with mouth cavity proper between incisor and cheek teeth and by small gaps between last molars.
Where are the three openings of the salivary glands into the oral cavity?
Parotid duct opens into vestibule at level of 2nd/3rd upper cheek tooth.

Mandibular duct opens onto floor of mouth at small sublingual caruncle, opposite the inferior canine teeth.

Sublingual gland drains into small ductules along sublingual fold, lateral to tongue along ventral floor.
Describe the hard palate.
Hard palate = bounded by alveolar processes and teeth; contains 2 symmetrical series of ridges.

Incisor papillae = located just caudal to central incisors; incisive duct communicates with nasal cavity and vomeronasal organ, but blind pouches on either side of papillae do not communicate with either cavity.

Mucosa contains large venous plexus which may become engorged at time of teeth replacement/eruption.
Describe the soft palate and its components.
Soft palate = caudal continuation from hard palate, at level opposite M3

- Separates nasopharynx (dorsally) and oropharynx (ventrally)
- at caudal end, it sits rostral-ventral to epiglottis, in contact with base of epiglottic cartilage
- with nasal endoscope, able to see the tip of epiglottis sitting dorsal to soft palate
- this relationship prevents oral breathing under normal conditions
- if horse is able to vomit (very rare), regurgitated food enters nasal cavity instead of mouth.

Mucosa contains pits (where the palatine glands open onto) and the rostral median tonsil (swelling).

Palatoglossal arch = mucosal fold extending from soft palate to root of tongue.

Palatopharyngeal arch = mucosal fold extending caudally along lateral wall of pharynx from caudal edge of soft palate to meet arch of opposite side just dorsal to esophageal orifice.
Describe the tongue and the associated tonsils.
Apex held loosely by narrow frenulum

Papillae located along dorsum of tongue

Dorsal and lateral surface contains numerous delicate filiform papillae

Fungiform papillae located along lateral sides of tongue (taste buds)

Larger vallate papillae located near root of tongue (taste buds)

Foliate papillae located just dorsal to palatoglossal arch as a rounded prominence (taste buds).

Lingual tonsil = diffuse structure of scattered lymphoid tissue located in crypts between elevations at root of tongue, lateral to median glossoepiglottic fold.
Name the three branches off of the common carotid a. (not including the external carotid a.). Where are they traveling to?
1) Cranial thyroid a. = ventral branch of common carotid a. at level of larynx

2) Internal carotid a. = arises caudodorsally and runs rostrally, medial to occipital a.; major blood supply to cerebrum
• Enters braincase via tympano-occipital fissure; loops out/in braincase at foramen lacerum
• Continues along ventral surface of brain to form cerebral arterial circle

3) Occipital a. = arises caudodorsally from a., just cranial to internal carotid a.; runs dorsally under wing of atlas.
• Anastomoses with vertebral a. (which coursed cranial through transverse foramina of cervical vertebrae) and continues cranially through lateral vertebral foramen of atlas
• Supplies smaller branches to brain.
Describe the linguofacial artery. Which artery does it branch from? Which arterial branches does it give rise to?
Linguofacial a. = initial ventral branch of external carotid a.; runs deep to its accompanying vein

Splits into:
a) Facial a. = accompanies parotid duct and facial v. as it runs dorsally along rostral border of masseter m.; able to take pulse from artery where it lies against ventral border of mandible
- gives off -
- Inferior labial a. = branches on lateral side of mandible and runs rostrally, deep to depressor labii inferioris m.
- Superior labial a. = branches just dorsal to superior arcade and runs rostrally
- Lateral nasal a. = branches near superior labial a. and runs rostrally, dorsal to superior labial a.
- Dorsal nasal a. = branches dorsal to infraorbital foramen and runs rostrally along dorsal nose
- Angularis oculi a. = continuation of a. that turns caudal and continues towards orbit

b) Lingual a. = ventral branch that runs rostrally within intermandibular space
Describe the masseteric artery. Which artery does it branch from? Where does it go?
Branch off of the external carotid artery.

Masseter a. = runs ventrally, crossing ventral border of mandible, and ascends in groove along rostral border of masseter m.; able to take pulse along this vessel’s subcutaneous portion, esp. in thin-skinned horses or Thoroughbreds
Caudal auricular artery
Caudal auricular a. = dorsal branch of external carotid a.
Courses to the caudal portion of the ear.
Superficial temporal artery and branches. Where does it come off of?
Superficial temporal a. = terminal branch of external carotid a.
Gives off the terminal branches:
- Transverse facial a. = emerges just dorsal to branching of buccal branches from CN VII; run rostrally, deep to masseter m.
- Rostral auricular a. = runs dorsally towards rostral base of ear
What are the two terminal branches of the external carotid artery?
Superficial temporal artery and maxillary artery.
Describe the maxillary artery and the branches it gives rise to.
•Maxillary a. = much larger terminal branch of external carotid a.; runs under caudal border of mandible

Gives rise to:
•Inferior alveolar a. = enters mandibular foramen and runs through mandibular canal

•External ophthalmic a.
- Supraorbital a. = runs toward supraorbital foramen between periorbita and bony orbit
- Lacrimal a. = runs towards and supplies lacrimal gland and palpebra

•Buccal a. - supplies the cheek.

•Infraorbital a. = continues rostrally within infraorbital canal; emerges from infraorbital foramen
- Malar a. = runs rostrodorsally between periorbita and bony orbit, towards medial angle of eye
2 main veins on the head that give rise to the external jugular vein.
•Big picture: external jugular v. receives drainage from linguofacial and maxillary vv., near caudal border of mandible

•Linguofacial v. = drains from facial and lingual vv.
- Facial v. = receives anastomoses from transverse facial, deep facial, and buccal vv. (see below); drains from dorsal and lateral muzzle and superior/inferior lips
- Lingual v. = drains from tongue, larynx, part of pharynx

•Maxillary v. = runs through parotid salivary gland along its course; drains ear, orbit, palate, nasal cavity, cheek, mandible, cranial cavity
Why does the veinous system dilate when the horse grazes? (I don't know how to put this fact into a question.)
•Dilations of venous drainage form the basis of a pumping mechanism—compression by masseter m. prevents stagnation of venous return from lowered head when animal is grazing.
Describe the transverse facial vein. Why is it clinically useful?
Transverse facial v. = dorsal-most anastomose with facial v., ventral to end of facial crest
- Begins superficial at caudal border of masseter m. and dives deep to m. along its rostral course; follows ventral edge of zygomatic arch
- CLINICALLY: this vein can be used for facial vein venipuncture: insert needle at 90° to surface of masseter m., just ventral to facial crest, at level of medial angle of eye
Describe the deep facial vein.
Deep facial v. = anatomose with facial v., ventral to level transverse facial v. anastomose

•Continues caudally, ventral to facial crest, and perforates ventral portion of periorbita

•Runs through orbital fissure, joins ophthalmic v., empties into cavernous venous sinus

•Monitored as part of heat control mechanism: serves to cool the internal carotid a. blood
Describe the buccal vein.
Buccal v. = ventral-most anastomose with facial v.
- runs caudally, deep to masseter m.
- runs along ventral border of buccinator and depressor labii inferioris mm
Describe the Auriculopalpebral nerve. Which CN does it come from? Why is it clinically important?
Facial nerve:
•Auriculopalpebral n. = motor to rostral auricular mm. and orbicularis oculi m.
•detaches from parent nerve before facial n. becomes superficial
•Palpebral branch = crosses ventral part of zygomatic arch (PALPABLE) towards orbicularis oculi m.
- Can be injured here.
Describe the Buccal n. (according to Dr. Hoffman = one nerve) or the ventral/dorsal buccal brr. (According to Rooney's)
•Dorsal and ventral buccal branches = branch from parent nerve after emergence from parotid gland & run rostrally
•these 2 branches are not always very distinguishable in all horses; variable appearance to branching

•PALPABLE as they cross superficial to masseter m.; usually visible through thin skin and easily damaged
- Trauma along the buccal branches is possible if left in lateral recumbency with halter still on

Clinical signs: dropping face, lips, ears; nose tilt (away from side with damage); ptosis possible
Describe the glossopharyngeal n.
oGlossopharyngeal n. (CN IX) = motor (GSE) and sensory (GSA) to pharyngeal mucosa and mm.; exits braincase at tympano-occipital fissure;

**runs medial to external carotid a., along mucous membrane of guttural pouch
Describe the cranial laryngeal n.
Cranial laryngeal n. = branches from vagus n. before caudal course in neck

•crosses lateral side of guttural pouch, runs rostroventrally, medial to origin of internal carotid a.

•runs through the thyroid foramen to enter larynx

•provides SENSORY innervation to laryngeal mucosa and motor innervation to cricothyroideus m.
- It is found at the dorsal aspect of the thyrohyoideus m.
Describe the caudal laryngeal n.
•Caudal laryngeal n. = continuation of the recurrent laryngeal n. = continuation of vagus n. after it branches and turns at level of heart to continue cranially

•left recurrent laryngeal n. encircles ligamentum arteriosum; right n. encircles right subclavian a.

•continues cranially associated with structures of carotid sheath (only enclosed within it for part of path)

•runs lateral to cricoarytenoideus dorsalis m. to enter larynx, medial to thyroid lamina

•innervates intrinsic mm. of larynx (except cricothyroideus m.) -- MOTOR!
Describe CN XII.
Hypoglossal n. (CN XII) = emerges from hypoglossal canal at caudal braincase; crosses LATERAL to external carotid a., near origin of linguofacial v.; provides motor innervation to extrinsic and intrinsic mm. of tongue
In general - locations of CN blocks for the head.
•block infraorbital n. as it emerges from infraorbital foramen → desensitize upper lip, nostril, and nose

•block infraorbital n. 2-3 cm within infraorbital canal → desensitize upper lip, nostril, nose, deep structures of face to level of medial angle of eye, superior incisor, canine and first 2 cheek teeth

•block mental n. as it emerges from mental foramen → desensitize lower lip and chin region

•block mental n. 3-5 cm within mental foramen → desensitize lower lip, chin, canine and incisor teeth

block auriculopalpebral n. between caudal end of zygomatic arch & base of ear → eliminates blinking, closing eyelids
What is the guttural pouch?
Guttural pouch = ventral diverticulum of the auditory tube
•formed by ventral slit between medial and lateral supporting cartilages of the auditory tube
•“droops” over the stylohyoid bone, which partially divides it into lateral and medial compartments
•Medial compartment sits more caudally, just ventral and rostral to base of ear
•Lateral compartment sits more rostrally
•located off of auditory tube, about 3 cm caudal to the pharyngeal opening of the auditory tube
•located partially superficial to temporohyoid joint
What are the boundaries of the guttural pouch?
•Dorsally: base of skull and atlas

•Ventrally: pharynx and beginning of esophagus (ventral floor mainly on pharynx and stylohyoid bone)

•Laterally: pterygoid mm. and parotid and mandibular salivary glands

•Medially: left/right pouches separated dorsally by ventral straight mm. of head & ventrally by thin median septum
Which structures are associated with the medial portion of the guttural pouch?
Neurovascular bundles are associated with medial compartment: CNs 9/10/11/12, sympathetic trunk, and internal carotid a. run within a fold in the (dorsocaudal recess of) medial compartment of guttural pouch
Which nerves are associated with the guttural pouch?
•Glossopharyngeal (CN IX) and hypoglossal (CN XII) nn. emerge from caudal base of skull and run rostrolaterally with stylohyoid bone, closely associated to medial pouch of guttural pouch
•Facial n. (CN VII) is minimally associated with dorsal part of pouch
•Clinically, we’re more concerned with (more common) damage to CNs IX and X; CN XII less often injured
•Sympathetic trunk (beyond cranial cervical ganglia) runs caudally from caudal base of skull; damage to this presents as Horner’s Syndrome (enophthalamus, ptosis, 3rd eyelid protrusion, myosis, facial sweating)
Which two arteries and vein are associated with the guttural pouch?
•Internal carotid a. is embedded in wall of medial pouch

•External carotid a. runs ventral to medial compartment, crosses lateral compartment laterally & rostrally

•Maxillary v. runs near to course of external carotid a.
What is the function of the guttural pouch?
It cools the horse’s brain: due to the extensive relationship between the cooler atmospheric air in the pouch and the warm arterial blood of the nearby extracranial internal carotid a., arterial blood is cooled as it enters the brain case, staying a more constant temperature, even during intense exercise
Where is the site of drainage of mucus secretion from rostral end of guttural pouch into nasopharynx?
= Pharyngotubal opening

•Opens naturally when horse swallows; drainage is favored during grazing
•Pouch distends when this drainage site is blocked, causing a visible and palpable swelling caudal to jaw
What are the boundaries of Viborg's triangle? What is its clinical significance?
•Boundaries of triangle: caudal border of mandible, tendon of insertion of sternocephalicus m., linguofacial v.

•When pouch is inflamed, it enlarges ventrally and becomes closely associated to this triangle

The triangle can be used to access the guttural pouch when distended/abscessed.

•modified Whitehouse approach: incise skin ventral and parallel to linguofacial v. (lateral approach)
•landmarks to avoid: parotid duct, linguofacial v., common and external carotid aa., CNs XII and IX
•can also access via reflection of parotid gland rostrally or via pharynx (using an endoscope)
Foals with malformation of the pharyngotubal opening -
presents as a externally-visible swelling
•caused by a redundancy of plica salpingopharyngea (mucosal fold at opening of tube)
•creates a one-way valve: air can enter but not exit the pouch
•fix by creating an artificial opening in median septum to allow communication between pharynx and both pouches
Describe the equine nostrils.
•Nostrils are large and widely spaced, supported by alar cartilages

•Alar cartilages form dorsal and ventral commissures

•Medial alar is concave ventrally and convex dorsally

•Nostrils and nasal cavity are very pliant, soft, and flexible; elliptical in shape when at rest

•Nostrils are able to dilate (obliterate fold and nasal diverticulum) during exercise, becoming more circular and decreasing air flow resistance

•Lamina of alar cartilage (from dorsal convexity of medial alar) connects caudally to alar fold
- This divides nostril into larger lower part and smaller upper part

•Nasal diverticulum = dorsolateral blind-ended pouch that extends caudally to nasoincisive notch; sits very superficially, caudal to nostril (Comparative anatomy: equine is only species with this)

•Lower/ventral part leads into nasal cavity

•Nasal septum = median section of cartilage covered in mucous membrane that serves to partially divide nasal cavity
Opening of nasolacrimal duct
Opening located along the ventral floor of nasal vestibule, near the mucocutaneous junction (junction of darkly pigmented skin with pink-tinted mucous membrane); site of drainage of tears
What are concha? What are the conchae within the nasal cavity?
•Concha = thin osseous scrolls covered by mucous membrane; very vascular in nature; serve to increase surface area and warm inspired air

•Dorsal and ventral conchae extend from lateral septum and coil in opposite directions

•Each space is divided into 2 subcompartments by an internal septum

•Caudal third of each nasal concha houses a conchal sinus
Dorsal concha sinus communicates with rostral extension of frontal sinus

Ventral concha sinus communicates with rostral maxillary sinus
•Ventral nasal concha has rostral extensions: alar (dorsal) and basal (ventral) folds
•Ethmoidal conchae located in dorsal-caudal portion of nasal cavity, against cribriform plate
What are the four nasal meatuses?
•Dorsal nasal meatus: channels air towards olfactory mucosa

•Middle nasal meatus: channels air towards nasal sinuses

•Ventral nasal meatus: largest compartment; only one that communicates with nasopharynx (resp passage)

•Common nasal meatus: common communication between other 3 meatuses
Conformation of horse's head
Conformation of head varies, depending on age, sex, and breed of horse

•Foal’s head has a “domed” contour matching outline of brain; with age, face lengthens and deepens
•Ventral margin of mandible may have swellings due to erupting teeth
•Frontal sinus enlarges with age, creating a smoother dorsal profile at junction of face and cranium
•Usually have (relatively) longer faces in: mature adults, stallions, heavy draft horses
•Arabians have a characteristic “dished” (concave contour) face
Facial crest
•Facial crest = ridge of bone along lateral aspect of skull; continuous caudally with zygomatic arch; extends between rostral margin of 4th cheek tooth and temporomandibular jt, parallel to dorsum of nose
Zygomatic arch
•Zygomatic arch = forms ventral and caudal margins of orbit; composed caudally by zygomatic process of frontal bone and zygomatic process of temporal bone; formed rostrally by temporal process of zygomatic bone and zygomatic process of maxilla bone; site of origin of masseter m.
Nasoincisive notch
•Nasoincisive notch = prominent angle between nasal & incisive bones; related to caudal extent of nasal diverticulum
- Palpable
Cricoid cartilage location - is it palpable?
•Cricoid cartilage of larynx palpable along ventral neck, caudal to palpable thyroid cartilage
Orbit of the horse
•Comparative anatomy: equine has a complete bony orbit; in carnivores, the orbit margin is completed by orbital lig.
Infraorbital foramen
located deep to levator labii superioris m., just caudal to halfway between facial crest and nasoincisive notch; site of exit of infraorbital n. (from CN V)
Mental foramen
Mental foramina = located deep to depressor labii inferioris m. at rostral end of mandible; site of exit of mental nn. (from CN V)
Supraorbital foramen
Supraorbital foramen = located at root of the zygomatic process of frontal bone, just dorsal to orbit; site of exit of supraorbital n. (from CN V)
Where can you take a pulse from the facial artery?
Can take a pulse from the facial a. as it runs dorsally in the groove along the rostral border of masseter m.
Where can you take a pulse from the masseteric artery?
Can take a pulse from superficial portion of masseteric a. at caudal border of mandible
Temporomandibular joint and its components
Temporomandibular joint = articulation between condylar process of mandible and mandibular fossa of zygomatic process of temporal bone; located rostral to palpable condylar process of mandible

•Intra-articular disc = located between expanded flat facets of mandibular condyle and articular tubercle of temporal bone; divides joint into lower and upper “levels”

•Lower level of joint allows for hinge movements (supported by tight joint capsule)

•Upper level of joint allows lateral and slightly protrusive movements (more spacious joint capsule)

•Fibrous lateral ligament and elastic caudal ligament support both levels of joint
Cranial nuchal bursa
Cranial nuchal bursa = located between funicular part of nuchal ligament and dorsal arch of atlas (inflammation of bursa = poll evil)
Atlanto-occipital space
Atlanto-occipital space = located dorsal to spinal cord, enclosed by the dorsally-located atlanto-occipital membrane
Cerebellomedullary cistern (cisterna magna)
Cerebellomedullary cistern (cisterna magna) = expansion of subarachnoid space enclosed by membrane extending from cerebellum to medulla; creates a possible site for collection of CSF fluid (must penetrate funicular part of nuchal ligament to access this site via injection through the atlanto-occipital space and joint)
Hyoid apparatus
Stylohyoid bone: long bone extending dorsocaudally to articulate (cartilaginous union) with petrous temporal bone
- Guttural pouch molds around this structure and is subdivided into medial and lateral compartments
- many cranial nerves (refer to flashcard) and the temporomandibular joint capsule are associated with this articulation
- moves back and forth with swallowing—can agitate sensitive structures of region

Epihyoid bone: small bone located at point of articulation between stylohyoid and keratohyoid bones

Keratohyoid bone: extends rostrodorsally from basihyoid

Basihyoid bone: crosses midline, just rostral to larynx, at articulation site between keratohyoid & thyrohyoid bones
- contains Lingual Process, which extends rostrally into base of tongue
- site of insertion of fused sternohyoideus and omohyoideus mm.

Thyrohyoid bone: extends caudodorsal from basihyoid; articulates caudally with rostral cornu of thyroid cartilage
-- Associated muscles:
- Sternothyroideus m.
Extends from 1st costal cartilage to thyroid cartilage
Action: pull tongue and larynx caudally

- Thyrohyoideus m.
Extends from thyroid lamina to basihyoid and thyrohyoid bones
- Innervated by hypoglossal n. (CN XII)
Temporohyoid osteoarthropathy
Can involve temporohyoid joint and stylohyoid bone

- Usually presents with neurologic signs, due to damage of neighboring CNs VII and VIII

Can cause undue stress to guttural pouch
- Can treat via ceratohyoidectomy or partial stylohyoidectomy
- Then, when animal swallows, the stylohyoid bone doesn’t move and can fuse
- Put animal in dorsal recumbency, incise parallel to mandible, isolate facial a. and CN XII, and remove bone
Epiglottis
Epiglottis = most rostral; closes opening into larynx (found at entrance of larynx); located dorsal to soft palate
- articulates with cuneiform process of arytenoid cartilage (aryepiglottic folds = extend from lateral edge of epiglottis to arytenoid cartilage)
- base articulates with rostral end of thyroid cartilage
Thyroid cartilage
Thyroid cartilage = U-shaped, with solid ventral portion; wraps around all other cartilages

- Thyroid foramen (ventral to rostral cornu) contains passage of cranial laryngeal n.
- Thyoid notch = located on ventral surface, caudal to ventral border of thyroid; site of attachment of cricothyroid ligament (extends caudally to attach to ventral arch of cricoid cartilage)
- Rostral cornu articulates rostrally with thyrohyoid bone
- Caudal cornu articulates with caudal part of cricoid cartilage
- Site of insertion of sternothyroideus m. (on ventral lamina)

Thyrohyoid membrane = extends from rostral border of thyroid to basihyoid and thyrohyoid bones
Arytenoid cartilage
Arytenoid cartilage = odd-shaped, paired cartilages

- Corniculate processes = rostral portion of cartilage (curves dorsal and caudally from the rostral border of cartilage); forms dorsal border of laryngeal opening
- Muscular process = dorsal projection from caudolateral surface; site of attachment of crycoartenoideus dorsalis m. and site of articulation with lamina of cricoid cartilage

- Vocal process = ventral projections; site of attachment of vocal fold
Cricoid cartilage
Cricoid cartilage = most caudal; forms complete ring (wide dorsally, narrow ventrally) with dorsal median ridge
- palpable caudally at articulation with trachea
- lateral border articulates with caudal cornu of thyroid cartilage
- rostral border articulates with muscular process of arytenoid cartilage

**cricotracheal ligament = extends between cricoid cartilage and 1st tracheal ring
Laryngeal cavity components
Vestibule = extends caudally from laryngeal opening to vocal folds

Glottic cleft = opening between vocal folds and arytenoid cartilages

Infraglottic cavity = extends caudally from caudal edge of vocal folds to beginning of trachea
Laryngeal opening
Laryngeal opening: formed dorsally by corniculate processes of arytenoids cartilages, laterally by vocal folds, and ventrally by epiglottic cartilage

Glottis = corniculate process + vocal folds + passage between (the opening and the structures forming the opening)

Glottic cleft = laryngeal opening itself
Laryngeal ventricle
Laryngeal ventricle = diverticulum of laryngeal mucosa
- Bounded laterally by thyroid cartilage; bounded medially by arytenoid cartilage
- Bounded rostrally by vestibular fold (more lateral) and caudally by vocal fold (more medial)

Vocal fold = extends from vocal process of arytenoid cartilage to midventral part of thyroid cartilage

Vestibular fold = extends from ventral part of thyroid cartilage to ventral part of arytenoid cartilage
Cricoarytendoieus dorsalis m.
Cricoarytendoieus dorsalis m. (most clinically relevant): crosses dorsal aspect of larynx

Extends from dorsal lamina/median ridge of cricoid cartilage to muscular process of arytenoid cartilage

Functions to pull the muscular processes of arytenoids cartilages laterally → vocal folds move laterally (abduct) → glottic cleft opens (this is the only intrinsic m. that dilates the glottis)
Hypsodont teeth components
Cementum = forms an external covering/coat around entire teeth and lines infundibulum

Enamel = covers erupted portion of tooth, deep to cementum, and borders the infundibulum

Dentine = composes majority of tooth

Pulp cavity = center region that contains nerves and vasculature; extends almost to apex of tooth
- as distal portion of pulp cavity is exposed, secondary (darker) dentine forms and covers infundibulum

dental star: initially visible as a linear shape, but becomes rounded with greater wear
- not a depressed area; does not contain a rim of cementum
- located on labial edge of tooth

Infundibulum is lined by enamel and contains a partially-filled depressed cavity (“cup”) filled with cement
- Enamel initially projects above the surrounding dentine so that the cup does not contact opposing tooth
- With age, the infundibulum is worn down → cup disappears
- With greater age, enamel spot remains: only visible as a rim of enamel around small dark area
Hypsodont teeth "grinding"
Cheek teeth and incisors have high crowns that serve to increase working life

- Due to delayed formation, cheek teeth are able to grow for many years before coming into wear
- Premolars are enlarged to better accommodate a forage diet
- Most of crown is initially embedded in jaw and gradually extrudes to compensate for loss due to wearing
- Enamel coat of incisor and cheek teeth is infolded to increase presented surface area of durable enamel
- Alternating softer/harder tissues of enamel and dentine on occlusal surface increases efficiency of grinding
- Attrition causes wear of cheek teeth by 2-3 mm/year; hypsodont teeth wear at different rates, which creates a rough surface that is optimal for grinding
Deciduous dentition
3-0-3)/(3-0-3)

(deciduous teeth are smaller but similar in structure to permanent teeth)
Permanent dentition
(3-1-3/4-3)/(3-1-3-3)

(variable presence of superior PM1 - "Wolf tooth")
Incisors
Incisors: curved lengthwise, creating a convex contour; roots are implanted such that they converge; superior and inferior incisor arches wear so that they meet at a more pronounced angle with age/wear
Canine teeth
Canine teeth: usually form in both sexes, but don’t erupt in mares; in males, these accumulate tartar quickly
Superior PM 1
Superior 1st premolar = wolf tooth = often vestigial, variable presence; often extracted (may help with fit of bridle)
Cheek Teeth
Cheek teeth = continuous row of premolar and molar teeth
- 1st and 6th cheek teeth are mostly triangular, while others are more rectangular

Superior teeth are wider and have a more complicated folding of enamel surface (have 2 infundibula that fill with cementum prior to eruption) ;inferior teeth are folded, but without infundibula

Most of cheek teeth occlude with 2 teeth in opposite arcade

- Occlusal surfaces: involves lingual edge of superior teeth, buccal edge of inferior teeth (superior arcade is placed more laterally); creates a ventrobuccal slope on occlusal surface
- With wearing, buccal edge of superior teeth and lingual edge of inferior teeth form sharp “points” due to differential wearing (floating: points are filed down to prevent mouth injuries)
- Cheek teeth erupt continuously

Superior teeth have 3-4 roots, separated from maxillary sinuses via thin plate of alveolar bone; with eruption, roots move ventrally and teeth move rostrally (sinuses enlarge with age)

During eruption of inferior teeth, caps (remnants of deciduous teeth) can prevent eruption and cause temporary swellings along the ventral margin of mandible
Naming of teeth
3 Incisors, 1 canine, 3 (or 4 in superior arcade) premolars, 3 molars

Modified Triadan nomenclature
First digit tells which arcade

When looking at horse, number arcades clockwise, starting at horse’s own right superior arcade

Permanent dentition
•Superior right = 100s
•Superior left = 200s
•Inferior left = 300s
•Inferior right = 400s

Deciduous dentition
•Superior right = 500s
•Superior left = 600s
•Inferior left = 700s
•Inferior right = 800s

•Last 2 digits tells which individual tooth
- Number incisors medial → lateral (01-03)

Canine= 04

- Number cheek teeth rostral → caudal (05-11)

1st premolar = 05 (“wolf tooth”; variable presence)

1st molar = 09
Aging of horses by their teeth - guidelines
Look at incisor teeth and ask yourself: Are teeth erupted? Are they in wear? Are there cups?

Eruption dates
- Deciduous teeth: I1 erupts at 6d; I2 erupts at 6 weeks; I3 erupts at 6 months

Permanent teeth: I1 erupts at 2 ½ years, I2 erupts at 3 ½ years; I3 erupts at 4 ½ years

Occlusal surfaces
- In young horses, teeth occlusal surfaces are wider side-to-side (oval shape)

With age, teeth become longer front-back
- Older horses have occlusal surfaces that appear as triangles elongated in labiolingual direction

Originally, oval occlusal surface of incisor has an intact enamel casing with a central depression (cup)
- “in wear” = occlusal surfaces are just making contact with opposing tooth; outer enamel has begun to wear (erodes first at labial edge); usually takes about 6 months from eruption to “in wear”
- “level” = occlusal surfaces are flat and in contact with each other

Inside layer of infundibulum still presents a depression (“cup”)

Inner/outer enamel rings are separated by region of dentine; entire outer enamel ring is in wear

Incisor teeth meet at a steeper slant with age (teeth are more straight dorsal-ventral when young)

Presence of cup (begins as depression filled with cementum; becomes level with age, then levels off and disappears)
- I1 cup is gone = 6 years old
- I2 cup is gone = 7 years old
- I3 cup is gone = 8 years old

Dental star appears with further wear along tooth, and persists after disappearance of cup and enamel spot

“hook” and Galvayne’s groove (labial surface) on I3 are less reliable determinants
- Hook is present at about 7 years of age
- Galvayne’s groove appears at about 10 years of age and becomes progressively deeper with age
- After about 8 years old, this is mostly just an educated guess!


Variation can be due to different diets, cribbing habits
Horse dental procedures
Remove “caps” = removal of retained deciduous cheek teeth

Teeth floating = grinding down the roughened edges of cheek teeth that form with normal wear

Extraction of cheek teeth
Length, curvature, and close fit inhibit pulling a single tooth past its neighbors easily

Instead, open the maxillary sinus and use a “punch” push tooth ventrally
Frontal Sinus (Concofrontal sinus)
Frontal sinus = located in dorsal part of skull in frontal bone; sits medial to orbit and dorsal to maxillary sinus
-- Right/left sinuses are divided via osseous median septum; ventral floor molds around ethmoid labyrinth

Extends rostrally from level of temporomandibular joint to rostral margin of orbit; extends laterally to root of zygomatic process of temporal bone

Extensive communication rostrally with dorsal conchal sinus (over the ethmoidal labyrinth) → referred to as the conchofrontal sinus

Frontomaxillary opening = communication point between frontal sinus and caudal maxillary sinus
- located medial to medial angle of eye, rostrolateral to ethmoid labyrinth
- allows for easy drainage of frontal sinus; creates indirect communication between frontal sinus and nasal cavity (caudal maxillary sinus communicates with middle nasal meatus)

•Surgical boundaries (similar size as sinus itself)
- Caudally: transverse plane through zygomatic process of frontal bone
- Rostrally: transverse plane halfway between rostral margin of orbit and infraorbital foramen
- Medially: line ~2 cm lateral and parallel to dorsal midline
- Laterally: line between supraorbital foramen and rostral end of medial limit
Maxillary Sinus (2 components)
Caudal and rostral maxillary sinuses = located in upper jaw, rostral and lateral to frontal sinus and closely related to roots of caudal cheek teeth
- Oblique osseous septum completely divides caudal and rostral maxillary sinuses
- located about 4-6 cm caudal to rostral end of facial crest
- normally no communication, although both open into the middle nasal meatus

ROSTRAL maxillary sinus
- Communicates with ventral concha sinus over the infraorbital canal
- Communicates with middle nasal meatus via nasomaxillary opening

CAUDAL maxillary sinus
- Divided into medial and lateral chambers by the infraorbital canal
- Medial chamber communicates freely with sphenopalatine sinus caudally
- Extensive communication with conchofrontal sinus via frontomaxillary opening
- Communicates with middle nasal meatus via nasomaxillary opening

•Contain projections of the roots of the last 3-4 superior cheek teeth
- Roots are covered by mucosa and thin layer of bone
- As teeth erupt (roots move ventrally), the maxillary sinus enlarges in older horses
Nasomaxillary opening
• Nasomaxillary opening = dorsally-placed, common communication point with middle meatus of nasal cavity
o Usually located ~5cm caudal to rostral end of facial crest
Main natural route of sinus drainage (entrance to all sinuses is via middle nasal meatus)
Frontomaxillary opening
Frontomaxillary opening = communication point between frontal sinus and caudal maxillary sinus
- located medial to medial angle of eye, rostrolateral to ethmoid labyrinth
- allows for easy drainage of frontal sinus; creates indirect communication between frontal sinus and nasal cavity (caudal maxillary sinus communicates with middle nasal meatus)
Surgical boundaries of the maxillary sinus
Surgical boundaries (more limited than sinus itself)
- Caudally: plane through rostral border of orbit
- Rostrally: line between rostral end of facial crest and infraorbital foramen
- Ventrally: facial crest
- Dorsally: line extending from infraorbital foramen, parallel to facial crest (nasolacrimal runs parallel and dorsal to this line)
Sinuses - Important concepts
Direct (extensive) communication between dorsal conchal sinus and frontal sinus → conchofrontal sinus

- At nasomaxillary opening, direct communication between rostral and caudal maxillary sinuses with middle nasal meatus (but 2 maxillary sinuses do not communicate here)

- At frontomaxillary opening, direct communication between caudal maxillary sinus and frontal sinus

- Direct communication between caudal maxillary sinus and sphenopalatine sinus

- Indirect communication between frontal sinus & middle nasal meatus via caudal maxillary sinus
Lateral retropharyngeal LNs
Lateral retropharyngeal LNs = located along caudodorsal surface of guttural pouch, ventral to wing of atlas (caudal and dorsal relative to medial retropharyngeal LNs); closely associated to internal carotid a., vagosympathetic trunk
- Drain similar structures as the larger medial retropharyngeal LNs
-Drain into medial retropharyngeal or cranial deep cervical LNs
Parotid LNs
Parotid LNs = located deep to rostral part of parotid gland (not normally palpable)
Mandibular LNs
Mandibular LNs = located in a spindle within the intermandibular space; right and left LNs are arranged as 2 elongated groupings that are joined rostrally but diverge caudally to form a V-shape
- Drain superficial structures of face, intermandibular space, mouth, and rostral nasal cavity
- Drain into medial retropharyngeal LNs or directly into cranial deep cervical LNs
Medial retropharyngeal LNs
Medial retropharyngeal LNs = located along lateral groove between pharynx and guttural pouch, medial to external carotid and linguofacial aa., digastricus m., and mandibular salivary gland
•Drain most of structures of dorsocaudal part of head and efferents from parotid and mandibular LNs (main collection point of lymph from upper head)
- Drain into cranial deep cervical LNs
NOTE: strangles infections (Streptococcus equi) often abscess here first
Parotid Salivary Gland
Parotid salivary gland = largest salivary gland (serous secretory gland)

Basically rectangular in shape
- Extends rostrocaudally between caudal border of masseter m.(and mandible) and wing of atlas
- Extends dorsoventrally between base of ear and angle between maxillary and linguofacial v.

Relation to other soft tissue structures
- Portion of gland is superficial to masseter m. and parotid LNs, ventral to temporamandibular jt

Deep surface of gland is related to guttural pouch, stylohyoid bone, muscles
- Separated from deeper mandibular gland by tendons of insertion of brachiocephalicus and sternocephalicus mm.
- Maxillary v. runs through gland
Parotid duct
Parotid duct forms at rostral mandibular angle of Parotid salivary gland
- Runs superficial to sternocephalicus m. tendon along ventral border of mandible
- Continues along rostral border of masseter m., caudal to facial a./v.
- Opens into vestibule at level of 2nd/3rd upper cheek tooth
Mandibular salivary gland
(mixed secretory gland)

Long and narrow in shape: located along curve, medial to angle of mandible and parotid gland
- extends dorsally from basihyoid bone to atlantal fossa
- ventral end lies deep to linguofacial v. and tendon of insertion of sternocephalicus m.
- superficial portion related to parotid gland and mm. of mastication
Mandibular duct
Mandibular duct forms at rostral margin of mandibular salivary gland

- runs rostrally, deep to mylohyoideus mm.; follows medial aspect of sublingual salivary gland
- opens onto floor of mouth at small sublingual caruncle, opposite the inferior canine teeth
Sublingual salivary gland
(polystomatic gland)
- located ventral to oral mucosa, between body of tongue and medial surface of mandible
- drains into small ductules along the sublingual fold, lateral to the tongue along ventral floor of mouth
Buccal glands
located as 2 rows along the dorsal and ventral margins of buccinator m.
Digastricus m.
Occipitomandibular part originates at paracondylar process of occipital bone and inserts on angle of mandible (caudal border of mandible and ventromedial part of molar region of mandible)
- Remainder of digastricus m. lies medially and inserts on ventral border of mandible
- Also has an intermediate tendon that runs through a split in the insertion of the stylohyoideus m.

Action: active opening of the mouth; raises hyoid apparatus and root of tongue
Depressor labii inferioris m.
(innervated by dorsal and ventral buccal branches)
- Originates in common with buccinator m. at alveolar margin and adjacent mandible, deep to masseter m.; runs rostrally over body of mandible to insert rostral to mental foramen

Tendon located superficial to palpable mental foramen at rostral end of mandible
- Inferior labial a. runs deep to muscle belly; mental nn. emerge deep to muscle belly
Levator labii superioris m.
(innervated by dorsal and ventral buccal branches)

Originates on lacrimal bone, rostral to eye; inserts in upper lip, between nostrils (within a synovial sheath)

Action: raise superior lip (Flehmen response)
- Located deep to levator nasolabialis m.
- Runs superficial to palpable infraorbital foramen (where infraorbital n. emerges)
Levator nasolabialis m.
(innervated by auriculopalpebral branch)

- Originates on frontal and nasal bones; extends ventrorostral to join orbicularis oris m.

Action: elevate upper lip, enlarges the nostril
- Located superficial to levator labii superioris m.