THE SPERMATIC DUCTS. 



237 



Lumen 



disposition of the circular fibres being disturbed by oblique bundles. The 

 mucous membrane is modelled by numerous ridges and depressions and 

 covered with a single layer of low columnar nonciliated epithelial cells. 



The Ejaculatory Duct. This, the terminal segment of the spermatic 

 canal, although apparently formed by the union of the duct of the seminal 

 vesicle and the vas deferens, is the morphological continuation of the vas, 

 from which, when still represented by the embryonic Wolffian duct, the 

 seminal vesicle develops as an outgrowth. The ejaculatory duct penetrates 

 part of the prostate gland and ends in the urethra by a minute opening sit- 

 uated on the urethral crest, at the side of the orifice of the prostatic utricle. 

 It possesses a structure essentially the same as that of other parts of the sper- 

 matic canal, its walls, however, being thinner than in the ampulla in conse- 

 quence of the diminished thickness and incompleteness of the muscle. On 

 reaching the ejaculatory duct the longitudinal muscle disappears and even 

 the remaining circular bundles become greatly reduced and intermingled 

 with fibrous tissue which almost replaces them. The surface of the duct, 

 particularly along its upper wall, is broken by minute depressions and diver- 

 ticula which recall, in miniature, those modelling the seminal vesicles. Some 

 of these are branched tubules and recall tubo-alveolar glands. The char- 

 acter of the epithelium is inconstant, in 

 places the lining being a single and in 

 others a double layer of low columnar 

 cells; within a short distance of the 

 end of the duct, the epithelium assumes 

 the transitional type found in the 

 prostatic urethra. 



The Seminal Vesicle. This 

 organ, one of a pair of sacculated 

 appendages of the spermatic ducts, 

 lies behind the bladder and in front 

 of the rectum. Its general form is 

 pear-shaped, with the base directed up- 

 wards and outwards and the abruptly 

 tapering lower end converging to join 

 the spermatic duct. When divested 

 of the fibre-muscular capsule that 

 blends the divisions into a knobbed 

 mass, the organ may be separated 

 into a chief duct and diverticula, all of 

 which, after repeated windings, end blindly. The lumen of the chief duct, 

 as seen in section (Fig. 289), is irregular, constrictions and dilatations 

 following one another with little order. The seminal vesicle contains a light 

 brownish fluid in which spermatozoa are usually found during the period 

 of sexual activity. 



In its general structure, the seminal vesicle resembles closely the ampulla 

 of the vas deferens, possessing a robust muscular coat composed of an inner 

 circular and an outer longitudinal layer of unstriped tissue. The mucous 

 membrane is conspicuously modelled by numerous ridges and pits, so that 

 in sections it appears honeycombed (Fig. 288). The surface of the larger 

 ridges is covered by two or three layers, that of the pits and diverticula by a 

 single layer, of low columnar epithelial cells, many of which contain secre- 

 tion-particles. Although definite glands are wanting, minute branched 

 tubular canals, lined with low columnar epithelium containing goblet-cells 



Pitted 



surface of 



mucous 



membrane 



FIG. 288. Cross-section of seminal vesicle, show- 

 ing modelling of mucous surface. X 12. 



