SCIENCE AND PRACTICE OF DAIRYING. 



developed net-work of capillary vessels (fig. 7), in which the 



material for the formation of milk circulates through numerous 



lymph tracts, and also by means of very fine nerve fibres, which 



promote special physiological functions of the glands. The duct- 

 lets, of which the alveoli are the dilations, 

 unite together among themselves in gradu- 

 ally ever-widening ducts the milk-ducts, 

 and end eventually in large hollow cavi- 

 ties, the so-called milk-cisterns or milk- 

 reservoirs (figs. 8-11). Four of these, which 

 lie above the teats, are present in each 

 udder, two on each side. The connective 

 tissue, which encloses the lobules of the 

 gland, and which unites them to the large 

 closed milk -glands, is 

 enveloped in adipose 

 tissue, and this in turn 

 is covered by the skin, 

 which is interspersed 

 with many blood-vessels. 

 On the udder there are, 

 as a rule, four teats 

 (fig. 12), corresponding 

 to the four milk-cisterns, 

 from which milk can 



be drawn; while behind them frequently occur 



some undeveloped teats, very rarely provided 



with outlet tubes. The duct of the teat 



(figs. 13-16) is about 4 millimetres in length, 



and is shut at its end by means of a smooth 



sphincter muscle. The capacity of both milk- 



glands, together with that of the four milk- 



reservoirs, in the udder of an average cow, after the left 8ide of the Udder 



' , . of a Dutch Cow, yielding 



milking, may be stated at about 6 to 7 cubic 3000 quarts of miik yearly 

 decimetres. 1 The internal space of the udder Haw natural size. (Fursten- 

 available for retaining milk, however, does not 

 admit of accurate estimation, owing to the great elasticity of the 

 surrounding tissue. The udder of a cow of ordinary milking capa- 

 city, carefully examined by us after slaughter, was found to have a 



About 10J to 11| pints. 



Fig. 9. Plaster of Paris Cast of 

 the Posterior Milk-cistern, with 

 the Canal of the Teat of the left 

 side, from the Udder of an Ayr- 

 shire Cow, yielding 1200 to 1300 

 quarts of milk yearly. Half 

 natural size. (Fiirstenberg.) 



