88 Anatomy and Physiology of the Mammary Gland. 



secutively with the numerals 1, 2, 3, &c. This illustration also 

 shows the manner in which the milk tubes are curved in their 

 course, and dilated here and there for the retention of the fluid 

 until the wants of the young animal cause its withdrawal in 

 the act of sucking. 



Besides this peculiarity we find another which is necessarily 

 connected with the arrangement of the lactiferous ducts that 

 we have described, namely, the existence of several passages in 

 the teat itself for the escape of the milk. It is necessary, lor an 

 easy comprehension of this matter, to explain that the latter are 

 anatomically designated mammillary tubes, and that their num- 

 ber is liable to great variation ; thus in the elephant and also in the 

 bitch we often find as manv as nine or ten, there being a correspond- 

 ing number (^f distinct sets of lactiferous ducts, in the substance 

 of the gland ; but in the pig rarely more than two mam.millary 

 tubes are met with. Evidence of this fact is afforded by the 

 simple act of pressing the teat, when the milk will be found to 

 escape from a greater or less number of points, each being in 

 reality the opening of a mammillary tube. In the mare also two, 

 or occasionally three, of these tubes exist ; but in the cow and 

 ewe only one. The tube in these latter named animals is of 

 large size, and capable of giving passage to a copious stream of 

 milk (see Fig. 6). 



Fig. 3. 



Shows the mammillary tubes (o, a) of the 

 elepliant, dissected from out of the substance of 

 the teat. It also depicts the openings of these 

 tubes {b), in tlie skin covering the ends of the 

 teat. An analogous arrangement of the tubes 

 is met with in the bitch. 



The illustration, Fig. 3, which we here insert, represents a 

 number of mammillary tubes, dissected from out of the teat, but 

 still kept together at their terminal portions by the common 

 integument at the extremity of the teat, where also their openings 

 are shown. 



We come now to speak more in detail of the intimate structure 

 of the mammae, and particularly in the cow. The secretion of 

 milk forms no exception to the rule which obtains with reference 

 to animal products in general, namely, that it is formed from 

 arterial blood. So large an amount of milk as is well known to 

 be furnished within a few hours by the cow, necessarily requires a 



