294 fascijE 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 nuchse, 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-scapular hgament, 

 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 fasciae 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 vertebrae. 



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 sepamtely, 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- 

 1 erficial branches of the ventral divisions of the cervical nerves. The mastoid part 



' This muscle is also called the mastoido-humeralis, humero-mastoideus, dero-brachialis and 

 levator humeri. 



