134 THE ARTISTIC ANATOMY OF ANIMALS 



the sternum, and is directed towards the angle formed by 

 the junction of the scapula and humerus ; then it is re- 

 flected upwards and backwards, to terminate on the 

 anterior margin of the shoulder by insertion into the 

 aponeurosis, which covers the supraspinatus muscle. 



We can, especially in the horse after removal of the skin, 

 recognise it, at the level of this region, in the interspace 

 limited by the superficial muscles (Fig. 70, 26). 



In the dog and cat this portion of the muscle does 

 not exist. The other division of the muscle, the sterno- 

 trochinian, is more interesting. It arises from the abdo- 

 minal aponeurosis and the posterior part of the sternum ; 

 hence it passes forward, turns under the superficial pectoral, 

 and is inserted into the lesser tuberosity (trochin) of the 

 humerus. 



In the pig, dog, and cat, it is inserted into the greater 

 tuberosity (trochiter) of the bone of the arm. 



The superior border of this muscle is in relation with 

 a superficial vein, which is distinctly visible in the horse — 

 the subcutaneous thoracic vein, which in this animal is 

 called the vein of the spur. 



The sterno-humeral muscle, in contracting, draws the 

 shoulder and the whole anterior limb backwards. 



Serratus Magnus (Fig. 67, 2 ; Fig. 69, 8 ; Fig. 70, 9). 

 — ^This muscle, which is situated on the lateral aspect of 

 the thorax, is covered to a considerable extent by the 

 shoulder, the posterior muscular mass of the arm, and by 

 the great dorsal muscle. 



It arises by digitations from the external surface of the 

 dorsal vertebrae ; from the first eight in the horse, ox, and 

 dog. 



The muscular bundles, converging as they proceed, to- 

 wards the scapula, pass under this bone, to be inserted 

 into the superior portion of the subscapular fossa, near 



' lesser pectoral ' in its sterno-prescapular portion. We do not consider 

 it necessary to give the other theories relative to the homologies of these, 

 notwithstanding the very real interest which they present from the 

 purely anatomical point of view, as they have but few appUcations in the 

 study of forms. 



