10 THE ANATOMY OF THE HORSE. 



It will be remembered that in the dissection of the pectoral region 

 the anterior deep pectoral could not be followed to its termination. 

 The reflected portion of the muscle is here seen (Plate 4), but is partly 

 covered by the insertion of the mastoido-humeralis. 



The Latissimus Dorsi (Plate 4). Though neither the origin nor 

 the insertion of the muscle is found here, attention should be given to 

 it as it is being exposed by the dissector of the back. It arises by an 

 aponeurotic tendon from the series of vertebral spines, beginning about 

 the 4th dorsal, and extending backwards to the last lumbar. This 

 tendon is succeeded by a thick muscular portion, which contracts and 

 passes in between the limb and the trunk, where it will afterwards be 

 followed to its insertion into the internal tubercle of the humerus. Its 

 anterior fibres will be noticed to play over the dorsal angle and cartilage 

 of prolongation of the scapula. 



Action. — It is a flexor and an inward-rotator of the shoulder-joint. 



The Rhomboideus (Plate 4), like the trapezius, comprises a cervical 

 and a dorsal portion. The cervical part is an elongated, narrow muscle, 

 which extends as far forward as the axis, and arises from the funicular 

 part of the ligamentum nuchee. Its fibres take a very oblique direction 

 downwards and backwards, and wee inserted into the anterior part of the 

 cartilage of prolongation on its inner surface, being there confounded 

 with the insertion of the levator anguli scapuke. The dorsal portion 

 consists of fibres which arise from the anterior dorsal spines, and pass 

 in a nearly vertical direction to be inserted into the inner surface of the 

 cartilage of prolongation, behind the fibres of the cervical division. It 

 will be recollected that the nerve to these muscles passes from the 6th 

 cervical nerve, and reaches its destination by traversing the levator 

 anguli scapula. 



Action. — To pull the scapula upwards and forwards on the chest-wall. 



The Mastoido humeralis, or Levator Humeri (Plate 4). This 

 muscle, in the greatest part of its extent, is found in the head and 

 neck, where it takes its origin from the mastoid crest and the trans- 

 verse processes of the first four cervical vertebra? ; but attention must 

 here be given to its insertion, which is into the anterior or external lip 

 of the musculo-spiral groove, after covering the shoulder-joint. It 

 receives here some branches from the circumflex nerve. 



Action. — It is an extensor and inward-rotator of the shoulder-joint. 

 When the limb is fixed it bends the neck laterally. 



Directions. — The limb may now be detached from the trunk by 

 severing the attachment of the rhomboideus, serratus magnus, levator 

 anguli scapuhe, mastoido-humeralis, and latissimus dorsi, the last being 

 cut where it plays over the angle of the scapula. Pieces of clean cloth 

 saturated with some preservative solution should be placed on the outer 

 aspect of the shoulder where the skin has been removed, while the 



