Anatomy and Physiology of the Mammary Gland. 93 



may add that the or^an receives a full supply of nervous filaments 

 from the lumbar plexus, which by their union with the nerves 

 of organic life, otherwise designated the ganglionic or sympathetic 

 system, provide for the special office of secretion as well as the 

 endowment of ordinary sensation. It is, however, unnecessary 

 that we should enter into any particulars of the course and distri- 

 bution of the nerves, or of the absorbents which belong to the 

 mamm^, and which likewise freely ramify in their substance. 

 We shall close our description of the anatomy of these glands 

 by a few remarks on the structure of the teats. 



The teats are four in number, or occasionally six, two being 

 superadded in connexion with additional mammary glands which 

 exist in some cows, but which as a general rule are imperiec tly 

 developed, and as such do not yield any supply of milk. The 

 teats are all of them directed more or less forwards and outwards, 

 so as to be conveniently placed for being seized by the calf when 

 sucking. This position is best seen in a heifer at the time of her 

 first calving, because from the subsequent long milking of the 

 animal the teats are often drawn into a position more directly 

 downwards ; a state of things well observed in old cows. In 

 point of size they vary a little, the two anterior ones exceeding 

 somewhat the dimensions of the two posterior. 



Each teat, As has been previously stated, is perforated by a duct 

 which communicates above with the milk reservoir, and is capable 

 of giving exit to a copious stream of the fluid. Tiiis mamoillary 

 duct is lined by a vascular mucous membrane, which has a thin 

 covering on its exposed surface of tessellated epithelium to defend 

 it from injury. The same membrane is continued into the 

 reservoirs and lactiferous tubes lining them throughout ; but in the 

 smallest ramifications of these, and also in their coecal extre- 

 mities, where the secretion of milk is effected, the epithelium is 

 modified into cells. Externally to the mucous membrane both 

 fibrous and yellow elastic tissue are met with, which by their free 

 interlacings make up the chief wall of the mammillary duct, and 

 give strength and. elasticity to it. At the terminal portion of the 

 duct these tissues are developed in increased quantity, and thereby 

 restrict the opening so that no milk can escape from the teat, 

 unless pressure is imparted from above to overcome this resistance. 

 A want of sufficient development of fibrous tissue at the end of the 

 teat, or a loss of its firmness of texture in some cows, becomes a 

 cause of the animal losing her milk when the reservoirs and ducts 

 are filled with the fluid. Various expedients are had recourse 

 to to remedy this state, of things, but none can be said to be 

 attended with perfect success. 



Externally the teats are covered with the common integument, 

 which is here without hair, and is also very tliin and pliable and 

 thrown into wrinkles. Between the skin and the true fibrous coat 



