TYPES AND MARKET CLASSES OF LIVE STOCK 157 



of the capsule inward from all sides to serve as a supporting 

 framework for the gland tissue and to form the milk cisterns 

 and ducts. 



Structure of the teat. The tissues of the capsule are pro- 

 longed downward, becoming greatly thickened, to form the 

 walls of the teats. The teat is cylindrical or conical in shape, 

 variable in length and diameter, and placed at the lowest por- 

 tion of the gland. Its shape and size are independent of the 

 size of the gland. It is very elastic and is covered with a tough, 

 close-fitting, thin skin. Through its center runs a duct called 

 the teat-canal, having a capacity, when distended, of from one 

 to one and one-half ounces in moderate-sized teats. There are 

 both circular and longitudinal muscle fibers, and at the lower 

 end the circular fibers form an involuntary sphincter muscle, 

 the function of which is to keep the teat-canal closed under 

 ordinary pressure. At the upper end of the teat is another 

 involuntary sphincter muscle, but it does not completely close 

 the canal, and sometimes a third is found farther above. The 

 sphincters are sometimes so relaxed that very slight pressure 

 is sufficient to open them, and the cow leaks her milk; of other 

 cows the reverse is true, making them hard milkers. 



The milk-cistern, ducts, and alveoli. Above the teat is 

 a reservoir, called the milk-cistern, seldom holding more than 

 half a pint. This cistern is divided into pockets of various 

 sizes into which the large milk-ducts empty. At the point of 

 entrance of these ducts are sphincter muscles, and while they 

 cannot entirely close the openings, they may very nearly do so, 

 and in this way the cow is enabled to "hold up her milk/' These 

 large ducts ramify to all parts of the gland and anastomose 

 (intercommunicate) freely; and at the intersections are still 

 other voluntary sphincter muscles. A strong effort on the part 

 of the cow is required to close the larger ducts in the lower part 

 of the udder, but a slight effort will close the smaller canals 

 further up in the glands. Cows differ greatly in their control 

 over these muscles and in their disposition to exert it. The 

 most common causes of holding up milk are fright, the presence 

 of strangers in the stable, lack of familiarity with surroundings, 

 irregularity in the time or manner of feeding or milking, and 

 sexual heat. With some cows it becomes a habit, much injuring 

 the usefulness and milking capacity of the animal. The large 

 ducts subdivide into smaller ducts, and these again into smaller 

 ones, until they terminate in groups of small sac-like bodies 



