198 



are such that one or more of the parts may become dis- 

 eased or deranged in function without involving the 

 other parts. Thus oiie or more of the lobules may for 

 some cause or otlier become deranged, and secrete blood 

 from the numerous capillary vessels which pass through 

 it and form the connecting links between the arterial 

 and venous circulation ; or the cellular tissue may break 

 down into albuminous serum or pus, which being dis- 

 charged w^ith the milk causes it to become ropy or forms 

 adherent strings which are ejected with the milk ; at the 

 same time all the other parts of the gland may be acting 

 normally. 



The glandular tissue consists of vesicles clustered like 

 grapes on a stalk around the finest lactiferous tubes or 

 smaller ducts, which are the ultimate terminations of the 

 lactiferous ducts. Each of these tubes forms a cul-de-sac 

 or a channel closed at one end, which opens into others 

 to form enlarged tubes which converge together, and 

 so on to form the lactiferous ducts. The vesicles {acini) 

 of the lobules as well as the tubes are lined with epithe- 

 lium or membranous tissue, which become infiltrated 

 with fat during lactation (figure 23, h). 



The lactiferous ducts are at first exceedingly numerous 

 but gradually converging, like the branches of a tree, 

 unite to form larger channels which flow into the sinuses 

 or milk reservoirs. 



The sinuses or reservoirs are situated just above the 

 base of the teat, and are usually two in number, one in 

 front and one behind, but sometimes in cows with highly 

 developed udder and milking capacity there are three or 

 four. They communicate with each other and are pro- 

 longed into the teat by separate and distinct excretory 

 terminal canals whose orifices are quite small and gather 

 at the end of the teat forming an outlet (figure 24). 



The excretory canals are larger at the upper part than 

 at the extremity; the orifices are usually behind on« 



