286 THE ANATOMY OF THE HORSE. 



between its main lobes, and on the mesial plane the elastic envelopes 

 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 galactopherous or lactiferous 

 sinus. The secretion of milk during the period of lactation is constant, 

 and the liquid accumulates in these reservoirs, to be drawn ofi" 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 subdivision 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 and 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, 



