222 NORMAL HISTOLOGY. 



The nipple is composed of fibrous tissue, with a considerable 

 admixture of elastic fibres, in which there are scattered bundles of 

 smooth muscular tissue lying parallel to the axis of the nipple. A 

 circular bundle of the same tissue is found at the base of the nipple, 

 and by its compression on the bloodvessels may be the cause of the 

 erection of the nipple. The skin at the base of the nipple and in 

 the areola surrounding it contains large sebaceous glands. 



The mammary gland in the male is functionless, and, while it 

 contains the same structures as in the female, it remains in a com- 

 paratively undeveloped condition. 



II. IN THE MALE. 



The male organs of generation include the penis, prostate, vesic- 

 ulse seminales, vasa deferentia, epididyrnis, and testes, together with 

 certain accessory glands. 



1. The Penis. This is formed by three parallel structures : the 

 corpora cavernosa, lying side by side and partially blending in the 

 median line, and the corpus spongiosum, situated beneath their line 

 of junction and containing the urethra. At its anterior end the 

 corpus spongiosum expands about the ends of the corpora cavernosa 

 to form the glans penis. These three bodies, except over the glans, 

 are firmly held together by fibrous tissue, which is condensed at 

 their surfaces to form compact sheaths or external coats enveloping 

 the erectile tissue of which each is composed. The sheaths of the 

 corpora cavernosa are incomplete where they are in contact, permit- 

 ting the erectile tissue to blend in the median line. This inter- 

 communication is freer toward the anterior end of the penis than 

 near its root, where the corpora cavernosa are more distinctly sepa- 

 rated, preparatory to their divergence to form the crura. 



The sheaths of the corpora cavernosa are composed of fibrous 

 tissue containing an abundance of elastic fibres. From its inner 

 surface each sheath gives off a number of fibrous bands, called 

 " trabeculse," which divide and anastomose with each other, forming 

 the chief constituent of the erectile tissue. Within these trabeculse 

 are numerous bundles of smooth muscular tissue. 



The erectile tissue is made up of these trabeculse, which give it a 

 spongy character and are covered with endothelial cells, converting the 

 spaces between them into cavernous venous channels. These become 

 engorged with blood during erection. The vessels supplying this blood 

 are situated in the trabeculse, and give off capillary branches, which 



