THORACIC LIMB. 



Because it affords the greatest convenience to the dissectors of other 

 parts of the body, the dissection of the thoracic limb should begin with 

 the animal on its back. In this position the pectoral region offers 

 itself for examination. 



The dissector should note the rounded prominence, formed by 

 the superficial pectoral muscle, extending from the cranial end 

 of the sternum to the limb. The prominence is bounded laterally 

 by the lateral pectoral groove, which marks the line of contact of 

 pectoral and brachiocephalic muscles. In the middle line, between 

 the pectoral prominences, is the shallow median 'pectoral groove, which 

 bifurcates at the manubrium of the sternum, the two limbs of the 

 groove diverging, each to join the lateral pectoral groove in the 

 shallow supraclavicular fossa. 



The position of the caudal border of the superficial pectoral muscle 

 is marked by a distinct fold of skin, but the limits of the deep pectoral 

 muscle cannot be defined on the surface of the body. 



Dissection. — Make an incision through the skin in the middle line 

 of the body extending the full length of the sternum. A second 

 incision, transverse in direction, should then be carried from the 

 sternum to the level of the elbow joint. The two flaps of skin thus 

 marked out must be raised from the underlying pectoral mass of 

 muscles. As this is being done, note must be taken of small cutaneous 

 nerves and vessels which pierce the pectoral muscles close to their 

 sternal attachment. Larger cutaneous nerves, derived from the sixth 

 cervical spinal nerve (n. supraclavicular is), will be seen crossing the 

 surface of the superficial pectoral muscle. 



Clean the surface of the superficial pectoral, taking care to preserve 

 a vein of some size (v. cephalica) and a small artery (a. transversa scapula) 

 which will be found at its cranial border. 



The thin fascia (fascia pectoralis) which covers the surface of the 

 pectoral muscles furnishes a layer that passes on to the lateral face 

 of the triceps muscle, and thence becomes continuous with the scapular 

 fascia. 



M. pectoralis superficialis. — The superficial pectoral 1 muscle is 

 generally described as divisible into two parts. The more cranial is 



1 Pectus [L.], breast, breast-bone. 



1 



