MYOLOGY 131 



THE MUSCLES OF THE TRUNK 



We shall divide them into muscles of the thorax, of the 

 abdomen, and of the back. 



Muscles of the Thorax 



The Pectoralis Major (Fig. 66, i, 2 ; Fig. 67, 3, 4 ; 

 Fig. 68, 7 ; Fig. 69, 10 ; Fig. 70, 11). — Further designated 

 by the name of superficial pectoral, this muscle is described 

 in treatises on veterinary anatomy as formed of two por- 

 tions : an anterior one, called the sterno-humeral muscle ; 

 the other, situated below and behind the preceding, bearing 

 the name of sterno-aponeurotic. 



It occupies the region of the breast, and, as a whole, it 

 takes origin from the median portion of the sternum, from 

 which it is directed towards the arm and forearm. 



The anterior portion (sterno-humeral muscle) — thick, 

 forming an elevation under the skin, and really constitut- 

 ing the pectoral region — is directed downwards and outwards 

 to be inserted into the anterior margin of the humerus 

 — that is to say, to the ridge which limits in front the spiral 

 groove of this bone. 



The other part (sterno-aponeurotic muscle) is situated 

 more posteriorly, and corresponds to the region known in 

 veterinary anatomy as the inter-fore-limb space, which is 

 limited laterally on each side by the superior portion of 

 the forearm, of which the point of junction with the trunk 

 bears the name ars. Arising from the sternum, as we 

 have above indicated, this portion is directed outwards, 

 to be joined with the terminal aponeurosis of the sterno- 

 humeral, and with that which covers the internal surface 

 of the forearm. 



All things considered, the sterno-humeral muscle may be 

 regarded as the representative of the upper fibres of the 

 great pectoral of man, of which the attachments, owing to 

 the more or less complete absence of the clavicle in the 

 domestic mammals, the fibres must be concentrated on the 



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