294 FASCL® AND MUSCLES OF THE HORSE 
Structure.—The cervical part is narrow, pointed at its anterior extremity, and 
lies along the funicular part of the ligamentum nuche, to which it is attached by 
short tendon bundles. The fibers are directed for the most part longitudinally. 
The thoracic part is quadrilateral in shape, and its fibers are nearly vertical. Its 
deep face is intimately attached to the dorso-scapular ligament. 
Relations.—Superficially, the skin and fascia (over a small area in front), the 
trapezius, and the cartilage of the scapula; deeply, the dorso-seapular ligament, 
the splenius, complexus, longissimus dorsi, and serratus dorsalis. 
Blood-supply.—Dorsal and deep cervical arteries. 
Nerve-supply.— Sixth and seventh cervical nerves. 
3. Latissimus dorsi.—This is a wide muscle which has the form of a right- 
angled triangle. It lies for the most part under the skin and cutaneous muscle, 
on the lateral wall of the thorax, from the spine to the arm. 
Origin.—The lumbo-dorsal fascia—and by this means from the lumbar and 
thoracic spines as far forward as the highest point of the withers. 
Insertion—The teres tubercle of the humerus, in common with the teres 
major. 
Action.—To draw the humerus upward and backward and flex the shoulder- 
joint. If the limb is advanced and fixed, it draws the trunk forward. 
Structure.-—The muscle arises by a wide aponeurosis, which fuses with that 
of the serratus dorsalis and with the lumbo-dorsal fascia. The muscular part 
is at first rather thin, but by the convergence of its fibers becomes thicker as it 
approaches the arm. The anterior fibers pass almost vertically downward over 
the dorsal angle of the scapula and its cartilage. The posterior fibers are directed 
downward and forward. The thick belly formed by the convergence of these 
passes under the triceps to end on the flat tendon of insertion, which is common 
to this muscle and the teres major. The tendon of insertion furnishes origin to the 
anterior part of the tensor fasciz antibrachii. 
Relations.—Superficially, the superficial fascia, skin, cutaneus, trapezius, 
and triceps; deeply, the cartilage of the scapula, the rhomboideus, the serrati, the 
external intercostals, and the lumbo-dorsal fascia. 
Blood-supply.—Subscapular, intercostal, and lumbar arteries. 
Nerve-supply.—Thoraco-dorsal nerve. 
B. VENTRAL DIVISION 
1. Brachiocephalicus.'—This muscle extends along the side of the neck from 
the head to the arm. It is incompletely divisible into two portions. 
Origin.—(1) The mastoid process of the temporal bone and the nuchal crest; 
(2) the wing of the atlas and the transverse processes of the second, third, and 
fourth cervical vertebre. 
Insertion.—The deltoid tuberosity, the curved rough line which extends from 
this almost to the distal extremity of the humerus, and the fascia of the shoulder 
and arm. 
Action.—When the head and neck are fixed, to draw the limb forward, ex- 
tending the shoulder joint. When the limb is fixed, to extend the head and neck, 
if the muscles act together; acting separately, to incline the head and neck to 
the same side. By means of its attachment to the strong fascia which extends 
from the deltoid tuberosity to the outer face of the elbow the muscle also acts as 
an extensor of the elbow joint (e. g., in standing). 
Structure.—As already mentioned, the muscle is capable of incomplete di- 
vision into two parts, the line of division being indicated by the emergence of sup- 
erficial branches of the ventral divisions of the cervical nerves. The mastoid part 
1 This muscle is also called the mastoido-humeralis, humero-mastoideus, dero-brachialis and 
levator humeri. 
