886 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



tubules, and by the constant formation of others behind them are gradually 

 pushed outward along the ducts. 



The Ducts of the Testis. The ducts of the testis (Fig. 306) comprise a 

 succession of tubes of different morphological and physiological values. 

 They are approximately twenty-five feet in length, and are named, in 

 order, tubuli recti, rete vasculosum, vasa e/erentia, canal of the epididymis, 

 vas deferens, and ejaculatory duct. The tubuli recti (t.r) and rete vasculosum 

 (r.v), being mere channels for the passage of spermatozoa, present no special 

 physiological features. The vasa efferentia (v.e) and the canal of the epididymis 

 (e) contain smooth muscular tissue in their walls, and, moreover, are lined 

 by ciliated epithelium, the cilia causing a movement outward ; both of 

 these features doubtless aid in the outward passage of the spermatozoa. 

 The excretory duct of the testis, or vas deferens (v.d), with its offshoot, the 

 seminal vesicle, is more important physiologically. It is nearly two feet in 

 length, with a diameter throughout the greater part of its course of one-tenth 

 of an inch. Near its termination, however, it is larger and sacculated, and 

 resembles the seminal vesicle ; it is known here as the ampulla of Henle. Its 

 epithelium is not ciliated, but its walls contain a very thick, plain muscular 

 layer consisting of outer longitudinal and inner circular fibres. In the walls 

 of the ampulla of Henle exist small tubular glands. The vas deferens is an 

 important storehouse for the spermatozoa. The glands near its termination 

 supply a part of the fluid of the semen. The muscles in its walls, by contract- 

 ing, aid in the seminal discharges. The seminal vesicle (v.s) is a branched diver- 

 ticulum from the vas deferens. In structure it is not radically unlike the 

 ampulla of Henle, its walls containing muscular layers and glands. Its chief, 

 if not its only, function is to contribute fluid to the semen. Of all the organs, 

 the seminal vesicles contribute probably the greatest share of fluid. Micro- 

 scopic examination does not confirm the old belief that the vesicles are store- 

 houses for semen, and this idea is now largely laid aside. The ejaculatory 

 duct (d.e) on each side is a short, thin-walled muscular tube, passing partly 

 through the substance of the prostate gland and serving to convey the semen 

 to the urethra. 



The Urethra. The urethra (Fig. 306, u), the common excretory duct 

 for the urine and the semen, is commonly described as consisting of three parts, 

 named, respectively, the prostatic, the membranous, and the spongy portions. 

 The first is characterized by the presence of the prostate gland, the second by 

 the absence of special features, and the third by the presence of Cowper's glands 

 and the penis. Throughout its length the wall of the urethra contains plain 

 muscular tissue arranged longitudinally within and circularly without ; and, 

 except at the external opening, the small racemose mucous glands of Littre. 

 Its wall is hence contractile and its lumen is kept moist. Beyond these its 

 special physiological features are given it by the organs above mentioned. 



The Prostate Gland. The prostate gland (Fig. 306, pr) is a compound 

 tubular gland whose alveoli are mingled with a large quantity of plain mus- 

 cular tissue. It completely surrounds the urethra at the base of the bladder, 



