Extrinsic Muscles Of The Thoracic Limb And Related Structures

Front 1

descending pectoral

Back 1

ORIGIN: The first sternebrae the fibrous raphe between adja- cent muscles.

INSERTION: The whole crest of the greater tubercle of the humerus.

ACTION: To adduct the limb when it is not bearing weight or to prevent the limb from being abducted when bearing weight.

INNERVATION: Cranial pectoral nerves (C7, C8).

Front 2

transverse pectoral

Back 2

ORIGIN: The first two sternebrae and usually a part of the third; the fibrous raphe between adja- cent muscles.

INSERTION: The whole crest of the greater tubercle of the humerus.

ACTION: To adduct the limb when it is not bearing weight or to prevent the limb from being abducted when bearing weight.

INNERVATION: Cranial pectoral nerves (C7, C8).

Front 3

deep pectoral muscle

Back 3

ORIGIN: The ventral part of the sternum and the fibrous raphe between fellow muscles; the deep abdominal fascia in the region of the xiphoid cartilage (the caudal end of the sternum).

INSERTION: The major portion partly muscu- lar, partly tendinous on the lesser tubercle of the humerus; an aponeurosis to the greater tubercle and its crest; the caudal part to the medial brachial fascia.

ACTION: When the limb is advanced and fixed: to pull the trunk cranially and to extend the shoul- der joint. When the limb is not supporting weight: to draw the limb caudally and flex the shoulder joint. To adduct the limb.

INNERVATION: Caudal pectoral nerves (C8, T1).

Front 4

brachiocephalicus

Back 4

ATTACHMENTS: All attachments are movable, but the clavicle or clavicular intersection is considered the origin for purposes of naming the muscles. The cleidobrachialis attaches to the distal end of the cranial border of the humerus. There is also a significant fascial tie into the axilla. The cervical part of the cleidocephalicus attaches to the cranial half of the mid-dorsal fibrous raphe and sometimes to the nuchal crest of the occipital bone. The mastoid part of the cleidocephalicus attaches to the mastoid part of the temporal bone with the sternomastoideus muscle.

ACTION: To advance the limb; to extend the shoulder joint and draw the neck and head to the side.

INNERVATION: Accessory nerve and ventral branches of cervical spinal nerves.

Front 5

sternocephalicus

Back 5

ORIGIN: The first sternebra or manubrium.

INSERTION: The mastoid part of the temporal bone and the nuchal crest of the occipital bone.

ACTION: To draw the head and neck to the side.

INNERVATION: Accessory nerve and ventral branches of cervical spinal nerves.

Front 6

sternohyoideus

Back 6

ORIGIN: The first sternebra and the first costal cartilage.

INSERTION: The basihyoid bone.
ACTION: To pull the tongue and larynx caudally. INNERVATION: Ventral branches of cervical

spinal nerves.

Front 7

sternothyroideus

Back 7

ORIGIN: The first costal cartilage.

INSERTION: The caudolateral surface of the thyroid cartilage.

ACTION: Same as the sternohyoideus—to draw the larynx and tongue caudally.

INNERVATION: Ventral branches of cervical spinal nerves.

Front 8

omotransversarius

Back 8

ATTACHMENTS: The distal end of the spine of the scapula; cranially, the transverse wing of the atlas.

ACTION: To advance the limb or flex the neck laterally.

INNERVATION: Accessory nerve.

Front 9

trapezius

Back 9

ORIGIN: The median raphe of the neck and the supraspinous ligament from the level of the third cervical vertebra to the level of the ninth thoracic vertebra.

INSERTION: The spine of the scapula.

ACTION: To elevate and abduct the forelimb. INNERVATION: Accessory nerve.

Front 10

rhomboideus

Back 10

ORIGIN: The nuchal crest of the occipital bone; the median fibrous raphe of the neck; the spinous processes of the first seven thoracic vertebrae.

INSERTION: The dorsal border and adjacent surfaces of the scapula.

ACTION: To elevate the forelimb and draw the scapula against the trunk.

INNERVATION : Ventral branches of cervical and thoracic spinal nerves.

Front 11

latissimus dorsi

Back 11

ORIGIN: The thoracolumbar fascia from the spinous processes of the lumbar and the last seven or eight thoracic vertebrae; a muscular attachment to the last two or three ribs.

INSERTION: The teres major tuberosity of the humerus and the teres major tendon.

ACTION: To draw the free limb caudally as in digging; to flex the shoulder joint.

INNERVATION: Thoracodorsal nerve (C7, C8, T1).

Front 12

serratus ventralis

Back 12

ORIGIN: The transverse processes of the last five cervical vertebrae and the first seven or eight ribs ventral to their middle.

INSERTION: The dorsomedial third of the scap- ula (serrated face).

ACTION: To support the trunk and depress the scapula.

INNERVATION: Ventral branches of cervical spinal nerves and the long thoracic nerve (C7).