CHAP. VIIL] ORGANS OF RESPIRATION AND SECRETION. 239 



18. "We have hither to considered various organs which could 

 be classed as alimentary or secreting organs, and some (like the 

 pancreas, &c.) which were both 

 alimentary and secreting struc- 

 tures, since they secreted a fluid 

 destined to assist in alimenta- 

 tion. Such secretions, however, 

 were always destined for the 

 service of the secreting or- 

 ganism itself, and to help its 

 own alimentary processes. But 

 we have now to consider organs 

 which are indeed both secre- 

 ting and alimentary, but which 

 secrete an aliment for the use 

 of another organism than that 

 which forms it. These are the 



MAMMARY GLANDS, Or breasts, 



Avhich secrete the milk destined 

 to nourish the young. Hitherto 

 we have met with a variety 

 of organs, but only with organs 

 which are pretty equally de- 

 veloped in every individual 

 cat. The mammary glands, 

 however, are parts which attain 

 a large size and perform an 

 important function, only in one 

 set of individuals of the species 

 we are occupied with namely, 

 in female individuals. These 

 glands form a considerable 

 mass, extending on each side 

 of the ventral surface of the 

 body, from near the axilla to 

 the hinder end of the abdomen. 

 Each gland is invested by 



fibrous tissue, which sends in septa (between the various parts of the 

 secreting glands), accompanied by much adipose tissue. The ultimate 

 structure of each gland consists of minute secreting cells bound up 

 by connective tissue into little "glandules," each giving out a small 

 duct, which originates from the cellules and then joins with others 

 to give rise to larger milk tubes, which ultimately end in certain 

 conical dilatations or "reservoirs" from which very small excretory 

 ducts extend forwards to a prominence or nipple, where they open 

 by minute apertures. 



The excretory ducts are formed of connective and elastic tissue, 

 with an epithelial lining of small columnar cells. 



Each nipple is highly vascular, and contains organic muscular 

 fibres, and its surface is beset with sensitive papilfe. There are 



) i 



Fig. 114. CAT'S MAMMARY GLANDS, WHEN 



FUNCTIONALLY ACTIVE. 



mg. Mammary glands. 



Teats. 



