998 GENERATIVE APPARATUS. 



escape of the milk ; it is by this prolongation that the young animal effects 

 suction. 



The two glands are fixed in their position by the skin which covers them, 

 and which is thin, black, covered with a line down, and altogether destitute of 

 hair in the vicinity of, or on, the teat, where the cutaneous surface is smooth, 

 greasy, and supple. They are also attached to the tunica abdominalis by several 

 wide, but short, elastic bands, which resemble the ligaments of the prepuce in 

 the male. 



Structure. — Structurally, the mammary glands offer for study : 1. A yellow 

 (elastic) fibrous envelope. 2. Glandular tissue. 3. The (jalactophorous (or lactiferous) 

 reservoirs or sinuses. 4. The excretory canals, or mammary (or milk) ducts. 



The elastic envelope, placed in the middle line, beside its fellow of the opposite 

 side, is mixed with the suspensory bands that descend from the abdominal tunic, 

 and sends into the substance of the gland a number of septa, which are inter- 

 posed between the principal lobules. 



The glandular tissue is a compound of gland-vesicles or acini, clustered in 

 groups around the lactiferous ducts. (The gland-vesicles are made up of an 

 amorphous membrane — membrana propria — lined with spheroidal nucleated cells. 



Fig. 537. Fig. 538. 



GLAND-VESICLES, WITH THEIR EXCRETORY ULTIMATE FOLLICLES, OR GLAND-VESICLES, 



DUCTS TERMINATING IN A DUCTUS LAC- WITH THEIR EPITHELIUM OR SECRETING 



TIFEROUS: FROM A MERCURIAL INJECTION CELLS, a, a, AND NUCLEI, 6, 6. 

 (magnified FOUR TIMES). 



They are -^ of an inch in diameter.) The lactiferous ducts commence by 

 blind extremities, and run into each other to constitute a certain number of 

 principal canals ; these open into the galactophorous sinuses (each a saccidus vel 

 sinus lactiferus). The glandular culs-de-sac are lined with a polyhedral epithe- 

 lium when the gland is inactive ; but during lactation the alveoli enlarge, their 

 walls become thickened by a regular epithelial layer, and their cavities filled with 

 spherical cells which are infiltrated by a great quantity of fat. 



Placed at the base of the teat, the galactophorous sinuses or reservoirs are 

 generally two in number, but sometimes there are three, and even four. They 

 nearly always communicate with each other, and are continued into the mam- 

 milla by an equal number of independent excretory canals — the definitive dmtSy 

 the orifices of which are very small, and are seen beside each other at the free 

 extremity of the teat. A fine mucous membrane lines the inner face of this 

 excretory apparatus ; it is doubled in the teat by a thick layer of tissue, which, 

 again, is covered by the skin that adheres closely to it. (Between the external 

 and internal tunic of the teats are found numerous fasciculi of unstriped 

 muscular fibres, arranged in a circular and longitudinal manner around these 

 ducts.) 



Connective and adipose tissue, vessels, and nerves complete this organization. 

 The arteries are from the external pudic trunk ; the veins are very numerous. 



