Formation of Milk. 37 



pail, wlien formed into milk, during the larger part of the 

 Embryo breeding period. 



To describe the exterior form of the udder would be 

 difficult, because of the frequent changes in its size, and 

 various degrees of its expansion. The udder skin or sack, 

 is composed of several elastic layers which supply the con- 

 tractive power of the skin, that enables the udder to ex- 

 pand when filling, by reason of its elasticity; and to con- 

 tract or shrink as it is emptied, by reason of its contract- 

 ility; the change in either direction, being made possible 

 only by the elastic structure of the skin. 



The interior of the udder consists of four quarters, each 

 of which contains a large gland, or milk-forming organ, 

 the gland and its enveloping fold forming a lobe in each 

 of the four quarters of the udder. The quarters, though 

 inclosed together, and loosely connected, are distinct and 

 separate as to their blood supply and milk forming action ; 

 each gland having its special blood-vessels and blood sup- 

 ply. The upper parts of the quarters are attached to the 

 walls of the pelvis and belly, being thus held up, or sus- 

 pended by their muscular attachments at the top of the 

 udder, and by which the udder is let down as its quarters 

 are filled with milk; each quarter, or the whole udder, 

 being drawn up by contraction, as each quarter, or the 

 whole udder, may be emptied by suckling or milking. 

 The glands of each quarter, or lobe, are in form similar to 

 a cluster of grapes, with branching tubes instead of stems; 

 the tubes having smaller branched extensions, as in the 

 branches of trees, the smaller extensions terminating in 

 follicles, which are small vessicles, or bags, with rounded 

 ends. Each gland is inclosed in a fold or sheath. See 

 rough outline in Plate III., Fig. 3. The cut may give a 

 fair idea of the general form of a section through the 

 center of a fore and hind quarter, forming one side, or 

 half, of a large udder when full, two lobes or quarters be- 



