34 



OBSTETRICAL ANATOMY. 



at its commencement, and narrow at its termination at the end of the teat. 

 The walls of the latter are very thick, elastic, and retractile. Not infre- 

 quently, there are found behind the four teats one or two rudimentary 

 teats, which are generally imperforate ; though in very rare instances they 

 have been observed to be perforate and to yield milk. 



The teats of the Cow are generally from two and a half to three and a 

 half inches in length, and, as has been said, this length varies according 

 as the animal has reared a large or small number of calves. The two an- 

 terior are generally the longest, and the corresponding quarters furnish 

 more milk than the others. The dartoid tissue around the free extremity 

 of the teat, acting as a sphincter, prevents the passive escape of the milk 

 from the orifices of the excretory ducts ; for if a small canula, scarcely 

 larger than one of these ducts, be inserted slightly beyond the orifice, the 

 secretion immediately flows. And when the end of a teat has been 

 incised, or when the elastic tissue of this part has been divided in the 

 performance of some operation, there is no longer any obstacle to the 

 emission of the milk. 



The arteries that supply the mammae of the Cow with blood are derived 

 from the external pudic. The branch of each side, on reaching the lateral 

 glands, divides into two principal trunks, one 6i which goes to a corre- 

 sponding quarter : that which is destined for the posterior gland bends at 

 a right angle backwards, the branch for the anterior quarter — the largest 

 — descending perpendicularly, to become subdivided into numerous ra- 

 muscules and terminal twigs. The veins and nerves are derived as in the 

 Mare. 



In the Cow, the secretion of milk can be excited and maintained by 

 regular " milking," the only suspension occurring before the birth of an- 

 other calf. 



Sheep and Goat. 



In the Sheep and Goat there are only two mammai, as in the Mare and 

 Ass, though they are formed on the same plan as in the Cow. They are 

 also inguinal, somewhat hemispherical and voluminous, particularly in the 



A 



A, Lobule of the Mammae filled with Milk ; B, Milk 

 Globules ; C, Colostrum: a, Cell with a visible 

 Nucleus ; b, Cells from which the Nucleus has 

 disappeared. 



Fig. 14. 

 Section of the Cow's Teat. 

 Principal Lactiferous Ducts ; b. 

 Lactiferous Sinus ; c c, Acini ; d, 

 Elastic or Dartoid Tissue of the 

 Teat ; e, Orifice of the Teat. 



