370 ACCESSORY MALE ORGANS. [BOOK iv. 



joined by the two vesiculce, seminales. Each vesicula is virtually a 

 long tubular diverticulum of the vas deferens, so coiled up as to 

 present a sacculated appearance, and its walls, though thinner than 

 those of the vas deferens itself, have the same general structure as 

 they have ; the internal surface, much folded, is like that of the vas 

 deferens lined by columnar non-ciliated epithelium. The cavity 

 serves as a temporary receptacle for the semen, though some 

 secretion, and in some animals a decided quantity, takes place from 

 its interior. In certain animals the secretion clots, and then ap- 

 pears to contain a substance identical with or allied to fibrinogen ; 

 in these animals the clot which is thus formed by the mixture of 

 the male secretion with the bloody secretion of the rutting female 

 helps to secure the retention of the former within the female 

 passages. 



The vas deferens and the duct or end of the vesicula seminalis 

 on each side join to form the common ductus ejaculatorius, which 

 passing through part of the prostate gland, opens into the prostatic 

 portion of the urethra. The prostate gland is composed of twisted 

 tubular alveoli lined with columnar epithelium, and of branched 

 ducts lined with shorter cubical cells ; its striking feature is the 

 presence of plain muscular fibres which are especially abundant 

 in the smaller septa, wrapping round the individual alveoli. The 

 prostatic portion of the urethra is lined with stratified epithelium, 

 the upper cells of which are flattened, and into this the cubical 

 epithelium of the prostatic ducts and the columnar epithelium of 

 the ejaculatory duct pass. The secretion of the prostate presents 

 no special features, except that it is apt to contain peculiar 

 concentric corpuscles ; but the fact that the prostate remains 

 undeveloped in castrated animals suggests that the secretion plays 

 some part in coitus. 



946. Erectile Tissue. The walls of the urethra consist of a 

 mucous membrane lined from the prostate onwards to near the 

 mouth with a stratified columnar epithelium, and strengthened by 

 plain muscular fibres disposed circularly and longitudinally. It 

 contains numerous small glands, and at its commencement two 

 large mucous glands, the glands of Cowper, affording a thick 

 mucous secretion. The tube thus constituted receives for some 

 little space in front of the prostate no special support, and is here 

 spoken of as the membranous urethra, but further on is supported 

 by a median column of erectile tissue, the corpus spongiosum, in 

 the axis of which it runs, as well as by two lateral columns of 

 erectile tissue, the corpora cavernosa, which meet in the middle 

 line above the medially placed corpus spongiosum and urethra. The 

 glans penis surrounding the end of the urethra is also essentially 

 a mass of erectile tissue. The structure of all these bodies is in 

 the main the same, the corpora cavernosa being distinguished by 

 possessing very stout capsules of fibrous tissue, and in some minor 

 features. 



