VAS DEFERENS. 787 



portion of the posterior border they pass out of the testicle, by twelve to fif- 

 teen openings, and are here called the vasa efferentia. 



Having passed out of the testicle, the vasa efferentia form a series of 

 small, conical masses, which together constitute the globus major, or head of 

 the epididymis. Each of these tubes when unravelled is six to eight inches 

 (15 to 20 centimetres) long, gradually increasing in diameter, until they all 

 unite into a single, convoluted tube, which forms the body and the globus 

 minor of the epididymis. This single tube of the epididymis, when unrav- 

 elled, is about twenty feet (6 metres) in length. 



The walls of the seminiferous tubes in the testicle itself are composed of 

 connective tissue and of peculiar structures which will be fully described in 

 connection with the processes of development of the spermatozoids. In the 

 rete testis it is uncertain whether the tubes have a special fibrous coat or 

 are simple channels in the fibrous structure. They are here lined with 

 pavement-epithelium. In the vasa efferentia and the epididymis, there is a 

 fibrous membrane, with longitudinal and circular fibres of non-striated mus- 

 cular tissue and a lining of ciliated epithelium. The movements of the cilia 

 are toward the vas deferens. In the lower portion of the epididymis the cilia 

 are absent. The tubular structures of the testicle, the epididymis and the 

 beginning of the vas deferens are shown in Fig. 286. 



At the lower portion of the epididymis, communicating with the canal, 

 there usually is found a small mass, formed of a convoluted tube of variable 

 length, called the vas. aberrans of Haller (i, Fig. 286). This is sometimes 

 wanting. 



Vas Deferens. The excretory duct of the testicle extends from the epi- 

 didymis to the prostatic portion of the urethra and is a continuation of the 

 single tube which forms the body and globus minor of the epididymis. It 

 is somewhat tortuous near its origin, and it becomes larger at the base of the 

 bladder, just before it is joined by the duct of the seminal vesicle. Near its 

 point of junction with this duct it becomes narrower. Its entire length is 

 nearly two feet (about 6 decimetres). 



The course of the vas deferens is in the spermatic cord, to the external 

 abdominal ring, through the inguinal canal, to the internal ring, where it 

 leaves the blood-vessels, passes beneath the peritoneum, to the side of the 

 bladder, then along the base of the bladder, by the inner side of the seminal 

 vesicle, finally joining the duct of the seminal vesicle, the common tube 

 forming the ejaculatory duct, which opens into the prostatic portion of the 

 urethra. 



The walls of the vas deferens are thick, abundantly supplied with vessels 

 and nerves, and provided with an external, fibrous, a middle, muscular, and 

 an internal, mucous coat. The greater part of that portion of the tube 

 which is connected with the bladder is dilated and sacculated. The fibrous 

 coat is composed of strong, connective tissue. The muscular coat presents 

 three layers ; an external, rather thick layer of longitudinal fibres, a thin, 

 middle layer of circular fibres, and a thin, internal layer of longitudinal 

 fibres, all of the non-striated variety. By the action of these fibres the ves- 



