Osteology Of The Thoracic Limb

Front 1

Clavicle

Back 1

CLAVICLE

Origin - L. 'clavis' key

Vestigial in the dog and cat, but more prominent in the cat.

Front 2

Scapula

Back 2

SCAPULA

Plural - scapulae

Origin - L.

The scapula is a flat, roughly triangular bone that is the most proximal bone of the thoracic limb. It is attached to the lateral aspect of the thorax through muscular rather than bony connections; this unique sort of articulation is referred to as a synsarcosis.

Front 3

Scapular shape

Back 3

SCAPULA

The triangular shape of the scapula is oriented with the base dorsal and slightly caudal and the apex ventral and slightly craniad. The base of the triangle is accordingly called the dorsal border, with cranial and caudal angles describing the points at which the margins of the scapula incline ventral to define the cranial and caudal borders, respectively.

Front 4

Scapular angles

Back 4

SCAPULA

Cranial
Caudal

Front 5

Scapular borders

Back 5

SCAPULA

Cranial
Caudal
Dorsal - The dorsal border is capped by a narrow band of cartilage in life, but is destroyed in drying.

Front 6

Scapular spine

Back 6

SCAPULA

The long axis of the scapula is sharply divided on its lateral face into cranial and caudal halves by a perpendicularly oriented scapular spine. The spine of the scapula provides attachment to the m. trapezius, m. omotarnsversarius, and the scapular part of the m. deltoideus.

Front 7

Acromion

Back 7

SCAPULA

Origin - Gr. 'acro' extremity + 'omos' shoulder

The scapular spine is enlarged at it distal extremity into the acromion. The knob-like acromion serves as attachment site for the acromial part of the m. deltoideus. Present in both the dog and the cat. The acromion has addition structures in the cat, including the hamate and suprahamate processes.

Front 8

Suprahamate process

Back 8

SCAPULA

Additional process on the acromion. Present in the cat, absent in the dog.

Front 9

Hamate process

Back 9

SCAPULA

Distal, caudal part of the acromion in the cat.

Front 10

Infraspinous fossa

Back 10

SCAPULA

The lateral aspect of the scapula caudal to the scapular spine. In life this flat region is filled with the m. infraspinatus.

Front 11

Supraspinous fossa

Back 11

SCAPULA

The lateral aspect of the scapula cranial to the scapular spine. In life this flat region is filled with the m. supraspinatus.

Front 12

Serrated face

Back 12

SCAPULA

The roughened region in the dorsal part of the medial scapula is the serrated face, which is the region on which the m. aerratus ventralis inserts.

Front 13

Subscapular fossa

Back 13

SCAPULA

The medial face of the scapula is relatively flat, constituting the subscapular fossa to which the m. subscapularis arises.

Front 14

Scapular neck

Back 14

SCAPULA

The most ventral (distal) part of the scapula (the apex of the triangle) is collectively called the ventral angle, and it is modified into an articular surface. The narrowed region proximal to the articulation defines the neck of the scapula, which features an especially deep scapular notch on its cranial aspect.

Front 15

Glenoid cavity

Back 15

SCAPULA

The concave surface of the ventral angle by which the scapula articulates with the humerous is called the glenoid cavity.

Front 16

Coracoid process

Back 16

SCAPULA

One of two small, indistinct processes in the region of the glenoid cavity on the medial side. Craniomedially, the coracoid process gives origin to the m. coracobrachialis.
Important for connection with the clavicle, therefore not very prominent in the cat and only slightly visible in the dog.

coraCoid - remember sCapula

Front 17

Infraglenoid tubercle

Back 17

SCAPULA

One of two small, indistinct processes in the region of the glenoid cavity on the medial side. Caudally, the m. teres minor arises from the faint infraglenoid tubercle.

Front 18

Supraglenoid tubercle

Back 18

SCAPULA

The supra glenoid tubercle is a protuberance on the cranial edge of the glenoid cavity and gives origin to the m. biceps brachii.

Front 19

Humerus

Back 19

HUMERUS

Plural - humeri

Origin - L.

The bone of the bracium is the humerus. Its proximal extremity articulates with te scapula at the scapulohumera (shoulder) joint via the humeral head.

Front 20

Head of the humerus

Back 20

HUMERUS

The head of the humerus is considerably larger then the complimentary area of the glenoid cavity. This fact contributes to the stability of the shoulder joint. The humeral head is also the most common site for development of sotochondrosis in the dog.

Front 21

Intertubercular (bicipital) groove

Back 21

HUMERUS

A deep intertubercular groove on the cranial aspect of the proximal humerous divides the greater and lesser tubercles. In life, the tendon of origin of the m. biceps brachii lies in the intertuberclar groove, where it is invested with an extension of the shoulder joint capsule that serves as a tendon sheath.

Front 22

Greater tubercle

Back 22

HUMERUS

The greater tubercle is the large, irregular prominence craniolateral to the humeral head. The m. supraspinatus and m. infraspinatus insert on the greater tubercle. The greater tubercle is a palpable bony landmark in the living animal, forming what is commonly called the “point of the shoulder.”

Front 23

Crest of greater tubercle

Back 23

HUMERUS

The greater tubercle describes an arc that is continued distal on the cranial aspect of the humerous. This creates the crest of the greater tubercle and provides attachment for the pectoral mm.

Front 24

Lesser tubercle

Back 24

HUMERUS

The lesser tubercle is an enlargement on the medial aspect of the proximal humerous, just cranial to the humeral head. The m. subscapularis inserts on this tubercle, as does part of the deep pectoral m.

The lesser tubercle (like the proximal, medial processes of the ulna) are lower than the lateral processes.

Front 25

Neck of the humerus

Back 25

HUMERUS

The humoral head attaches to the body of the humerous by a short, thick neck.

Front 26

Teres minor tuberosity

Back 26

HUMERUS

Near the proximal end of the tricipital line is a very indistinct teres minor tuberosity that represents the site of insertion of the m. teres minor.

Front 27

Tricipital line

Back 27

HUMERUS

A distinct ridge passes from the caudal part of the greater tubercle distal on the lateral aspect of the humerus. This is the tricipital line, which marks the edge of the attachement of the lateral head of the m. triceps brachii.Distal to teres minor tuberosity, proximal to deltoid tuberoisity.

Front 28

Deltoid tuberosity

Back 28

HUMERUS

The crest of the greater tubercle and the tricipital line converge near the middle of the humerous on its lateral aspect in a projection called the deltoid tuberosity. This is the insertion site for the m. deltoideus.

Front 29

Teres major tuberosity

Back 29

HUMERUS

Distal to the lesser tubercle on the medial aspect of the body is an indistinct enlargement, the teres major tuberosity, on to which the m. teres major inserts.

Front 30

Body of the humerus

Back 30

HUMERUS

Surfaces –
Cranial
Lateral
Caudal
Medial

Front 31

Brachialis (brachial, musculospiral) groove

Back 31

HUMERUS

The body of the humerus possesses a smooth surface that begins on the caudal aspect and spirals to the craniolateral aspect of the bone. This is the brachial groove, against which lies the m. brachialis.

Front 32

Humeral condyle

Back 32

HUMERUS

The humeral condyle is the distal end of the humerus and comprises two articular masses and the adjacent processes.

Front 33

Trochlea

Back 33

HUMERUS

The more medial articular surface is the trochlea, which articulates with both the head of the radius and the trochlear noctch of the ulna.

Front 34

Capitulum

Back 34

HUMERUS

The capitulum is the smaller, more lateral part of the articular surface, and it articulates with the head of the radius. The capitulum, through its articulation with the radius, represents the primary weight-bearing portion of the distal humerus.

Front 35

Epicondyles – lateral and medial

Back 35

HUMERUS

On each side of the condyle are irregular masses, the medial and lateral epicondyles. The medial epicondyle is more massive than the lateral and gives origin to the caudomedial muscles of the antebrachium (the flexor group).

Front 36

Lateral supracondylar crest

Back 36

HUMERUS

Passes proximal and medial from the lateral epicondyle. The lateral epicondyle and supracondylar crest give origin to the crainiolateral muscles of the antibrachium and the m. ancones (the extensor group.)

Front 37

Olecranon fossa

Back 37

HUMERUS

When viewed from the caudal aspect, a deep olcranon fossa lies between the medial and lateral epicondyles. The anconeal process of the ulna projects into this fossa during extension of the elbow.

Front 38

Radial fossa

Back 38

HUMERUS

The olcranon fossa is open to the radial foss on the cranial side of the condyle via the supratroclear fossa.

Front 39

Supratrochlear foramen

Back 39

HUMERUS

The bone within the olecranon fossa is usually perforated by the supratroclear foramen. This aperature represents a diminution of unneeded bone mass and no structures pass through it. Present in the dog, absent in the cat.

Front 40

Supracondylar foramen

Back 40

HUMERUS

Present in the cat, absent in the dog.

Front 41

Radius

Back 41

RADIUS

Plural - radii

Origin - L.

Meaning - spoke (of a wheel)

The radius is divided into a head, a body, and a distal extremity sometimes referred to as the trochlea.

Front 42

Head of the radius

Back 42

RADIUS

The head of the radius bears two distinct articular surfaces.

Front 43

Fovea capitis

Back 43

RADIUS

A concave articular fovea, the fovea capitis, that articulas with the capitulum of the humerus.

Front 44

Articular circumference

Back 44

RADIUS

A caudal articular circumference by which the radius articulates with the radial notch of the ulna.

Front 45

Body of the radius

Back 45

RADIUS

The body of the radius is roughly oval in cross-section. Its cranial surface is convex and caudal surface is more concave.

Front 46

Radial tuberosity

Back 46

RADIUS

Just distal to the neck on the medial aspect is a small enlargement called the radial tuberosity onto which one of the two tendons of the m. biceps brachii inserts.

Front 47

Trochlea of the radius

Back 47

RADIUS

The trochlea of the radius is called so because of the extensor grooves on its cranial surface, emphasizing the rold of the distal extremity as a pulley for the extensor tendons.

Front 48

Ulnar notch

Back 48

RADIUS

The ulnar notch is a small incisure of the lateral aspect of the distal extremity. This articulates with the adjacent ulna.

Front 49

Medial styloid process

Back 49

RADIUS

The medial side of the distal radius forms a distinct point called a styloid process. This process participates in the antebrachiocarpal joint and also gives origin to the short medial colleral ligament.

Front 50

Ulna

Back 50

ULNA

Longer bone of the antibrachium.

Front 51

Olecranon

Back 51

ULNA

The ulna is markedly larger at its proximal extremity than distal. The proximal end is expanded into a robust lever, the olecranon, to which the triceps brachii m. attach. The olcranon forms a prominent, palpable bony landmark, commonly called the point of the elbow in the living animal.

Front 52

Trochlear notch

Back 52

ULNA

The ulna articulates with the trochlea of the humerus via its deep troclear notch.

Front 53

Anconeal process

Back 53

ULNA

The most proximal protusion from the trochlear notch is the anconeal process, which projects into the olecranon fossa of the humerus when the elbow is in extension. In most dogs, the anconeal process form from a separate ossification center that fuses with the rest of the ulna around 4 months of age. Failure to fuse is a very common cause of elbow dysplasia.

Front 54

Radial notch

Back 54

UNLA

The distal end of the trochlear notch intersects a second, transversely oriented notch, the radial notch, which articulates with the articular circumference of the radius.

Front 55

Coronoid processes (medial and lateral)

Back 55

UNLA

The medial and lateral ends of the radial notch form two sharp medial and lateral coronoid processes. Osteochondrosis of the medial coroniod process (“fragmented coronoid process”) is a common cause of elbow dysplasia.

The medial coronoid process (like the proximal, medial processes of the humerus) are lower than the lateral processes.

coroNoid - remember ulNa

Front 56

Ulnar tuberosity

Back 56

ULNA

A small elevation, the ulnar tuberosity, can be identified distal and caudal to the medial coronoid process. The ulnar insertion of the m. biceps brachii inserts on this tuberosity.

Front 57

Body of the ulna

Back 57

ULNA

The body of the ulna is laterally compressed proximally and tapers into a narrow cylinder distally.

Front 58

Interosseous border

Back 58

ULNA

The face of the body adjacent to the radius constitutes the interosseous border, to which in life is attached an inerosseous ligament uniting these two bone of the antebrachium.

Front 59

Lateral styloid process

Back 59

ULNA

The body of the ulna tapers distal to the styloid process. The styloid process participates in the antebrachiocarpal joint and gives attachment to the short lateral collateral ligament of the carpus.

Front 60

Carpus

Back 60

CARPUS

The proximal row of carpal bones consists of (from medial to lateral) the radial, ulnar, and accessory carpal bones. The distal row is numbered from medial to lateral: first, second, third, and forth carpal bones. Note that in the palmar view, the first carpal bone overlies the second carpal bone.

Front 61

CARPUS

Radial (intermedioradial) carpal bone

Back 61

CARPUS

The big one, medial

Front 62

Ulnar carpal bone

Back 62

CARPUS

The small one, lateral

Front 63

Accessory carpal bone

Back 63

CARPUS

“The doorknob”, most distal

Front 64

First carpal bone

Back 64

CARPUS

Caudal to the second carpal bone

Front 65

Second carpal bone

Back 65

CARPUS

Cranial to the first carpal bone

Front 66

Metacarpal bones (I-V)

Back 66

METACARPUS

The metacarpal bones are numbered I-V (first, second, third, fourth, and fifth), with I being most medial. These are rod-shaped bones, with I being markedly shorter than the others. Each bone posses a proximal base, a body, and a distal head.

Front 67

Proximal palmar sesamoid bones

Back 67

PHALANGES

Each metacarpophalangeal joint is distinguished by two palmer sesamoid bones, embedded within the tendons of insertion of the mm. introssei. There is only one palmar sesamoid bone in the first metacarpophalangeal joint.

Front 68

Dorsal sesamoid bones (may not have been preserved with your specimen

Back 68

PHALANGES

Four small dorsal sesamoid bones (none for the first digit) are embedded in the common digital extensor tendons as they pass over the metacarpophalageal joints.

Front 69

Phalanges

Back 69

The canine forepaw consists of four fully developed, weight bearing digits and a small deial first digit (“pollex” or “dewclaw”). With the exception of the dewclaw, each digit comprises three phalanges. The dewclaw possesses only two phalanges.

Front 70

Proximal phalanx

Back 70

PHALANGES

P1.

The proximal phalanx of each digit is the longest.

Front 71

Middle phalanx

Back 71

PHALANGES

P2.

The middle phalanx is similar in shape to the first.

Front 72

Distal phalanx

Back 72

PHALANGES

P3.

Front 73

Ungual crest

Back 73

PHALANGES

The distal phalynx is modified by and ungual crest, associated with the tissues that produce the claw.

Front 74

Ungual process

Back 74

PHALANGES

A curved process arises from beneath the crest. This is the ungual process to which the wall of the claw attaches.

Front 75

Extensor process

Back 75

PHALANGES

Do not need to identify. The rounded dorsal part of the base of the distal phalanx is the extensor process on which the common digital extensor tendon is inserted. Not very prominent in the dog and cat.

Front 76

Flexor tubercle

Back 76

PHALANGES

A small process on the palmer surface of the distal phalanx is the flexor tubercle for insertion of the deep digital flexor tendon.