The: Abdominal Wall. 113 



II. THE ABDOMINAL WALL. 



1. Place the animal in the supine position. Make a median in- 

 cision of the skin of the ventral surface extending from the pubic 

 symphysis to the tip of the mandible, being careful not to cut through 

 more than the skin itself. Make three transverse incisions on the left 

 side, the first on the medial surface of the arm and extending to the 

 elbow, the second midway between the anterior and posterior limbs, the 

 third on the medial surface of the thigh and extending to the knee. 

 Work the flaps loose from the surface, using the handle of the scalpel, 

 until the side of the trunk is well exposed. On the right side of the 

 body it is sufficient to clear the middle line. Identify the structures 

 as follows: 



On the skin : 



(a) The thick compact connective tissue forming the corium. 



(b) The imbedded hair-follicles. 



(c) The loose subcutaneous tissue (tela subcutanea) by which 

 the skin is attached. 



(d) In the female: the mammary glands (mammae), forming a 

 layer on the inner surface, and more or less closely aggregated 

 about the mammary nipples. 



On the exposed surface: 



(e) The linea alba, a white aponeurotic line extending from the 

 pubic symphysis to the xiphoid process of the sternum. 



(f) The cutaneus maximus muscle, a thin sheet of muscle fibres 

 covering the entire lateral surface of the thorax and abdomen. 

 Origin : The linea alba, the ventral surface of the sternum in 

 its posterior portion, and the humeral spine. The last- 

 named portion appears on the medial surface of the humerus. 

 Insertion: The skin of the dorsolateral surface of the trunk. 

 The fibres are directed upward and backward. The muscle 

 is continuous across the back with its fellow of the opposite 

 side, and is extended backward to the dorsum of the tail. It 

 is used in shaking the skin. 



The artery passing forward for a short distance in the inguinal region, 

 and lying in the subcutaneous tissue, is the superficial epigastric, a 

 branch of the femoral (p. 149). 



The abdominal vein, a conspicuous vessel in the female, traverses the 

 lateral portion of the abdominal wall from the inguinal furrow to the 

 axillary fossa, lying on the external surface of the cutaneus maximus. It 

 is a tributary of the inferior epigastric (p. 134), and anastomoses forwards 

 with the external mammary vein of the axilla. The corresponding 

 arteries are the external mammary branch of the long thoracic (p. 137), 

 and the abdominal branch of the inferior epigastric, the latter arising 

 directly from an external spermatic trunk. 



The inguinal lymph nodes (lymphoglandulae inguinales) are small, 

 oval, brownish bodies lying in the inguinal furrow. 



