DISSECTION OF THE ABDOMEN. 295 



of the two glands are applied together and form a kind of intermediate 

 septum. A few strong slips of the same texture descend into the gland 

 from the abdominal tunic, and play the part of suspensory ligaments. 



The secretory structure of the gland is arranged on the racemose 

 type. If a bristle be passed into one of the orifices seen at the 

 extremity of the teat, it will pass upwards by the large milk duct, 

 and enter a dilatation at the base of the teat, termed the galacto- 

 pherous or lactiferous sinus. The secretion of milk during the period 

 of lactation is constant, and the liquid accumulates in these reser- 

 voirs, to be drawn off by the young animal. The milk ducts and the 

 sinuses are lined by a mucous membrane ; and in the substance of the 

 teat, between this mucous lining and the external skin, there are 

 some fibres of non-striped muscular tissue, arranged both longitudinally 

 and circularly. The circular fibres prevent the escape of the milk from 

 the sinus. 



The milk enters each sinus from a number of tubes which when 

 traced into the substance of the gland divide and subdivide, and the 

 smallest ducts resulting from this division lead up to the ultimate 

 acini of the gland structure. These acini are lined by a secretory 

 epithelium by whose agency the milk is formed. 



The arteries and veins of the glands are branches of the external 

 pudic vessels. They undergo a great increase in size during lactation. 

 The nerves of the gland are branches of the inguinal nerves. 



Directions. — Reflect the skin as shown in Plate 38. If the dissector 

 of the fore limb be engaged with the pectoral region, the skin from the 

 posterior part of that region will be turned back in a piece with that 

 over the front of the abdomen. If not, the dissector of the abdomen 

 must limit the skin which he is about to reflect, by an incision carried 

 outwards from the ensiform cartilage to the point of the elbow. He 

 will be guided in the same way towards the hind limb. Care must be 

 taken not to reflect the panniculus with the skin. 



A slight degree of tympanitic distension of the intestines is favourable 

 for the dissection of the abdominal wall. When excessive, however, as 

 it often becomes, it interferes with the dissection, and is almost certain 

 to rupture the diaphragm, or the abdominal wall before its dissection 

 can be completed. This should be prevented by tapping the large 

 intestine with a canula or trochar, making the puncture at the most 

 prominent part. 



Cutaneous Nerves. In reflecting the skin a multitude of small 

 nerves will be seen on its inner surface. They are derived from 

 the intercostal nerves. 



The Subcutaneous Abdominal Artery (Plate 38). Look for this 

 vessel near the middle line, in the region of the prepuce or mammary 

 gland. It is one of the terminal divisions of the external pudic artery, 



