502 THE REPRODUCTIVE SYSTEM 



The interlobular and the smaller intralobular ducts are also lined 

 by a single layer of columnar cells. Their wall is supplied with smooth 

 muscle, most of whose fibers have a longitudinal direction. The two 

 ducts of Cowper's glands open into the bulbous portion of the urethra. 



Associated Vestigial Structures 



The vestigial structures associated with the male reproductive system 

 include the appendices testis and epididymis, the superior and inferior duc- 

 tuli aberrantes, the paradidymis and the sinus pocularis. Of these it may 

 be said in general that they are more or less variable with respect of gross 

 and microscopic structure and even with respect of presence; that they 

 resemble histologically the structures with which they are homologous, and 

 that they tend to become cystic. 



The APPENDIX TESTIS is the least variable of the vestigial associates. It 

 is present in about ninety per cent, of cases. It is a small spherical, fre- 

 quently pedunculated, sac attached to the superior pole of the testis ; it is 

 covered with tunica vaginalis and lined with simple columnar epithelium, 

 sometimes ciliated, and represents the end of the degenerated fetal Miil- 

 lerian duct. 



The APPENDIX EPIDIDYMIS is a very similar pedunculated structure, much 

 less frequently present. It is situated on the globus major of the epididy- 

 mis. It is supposed to represent a degenerated Wolffian tubule. By some 

 it is regarded as the atrophic end of the Wolffian duct. 



The DUCTULI ABERRANTES are blind tubules, the remnants of meso- 

 nephric tubules which failed of inclusion among the ductuli efferentes of 

 the globus major. The superior ductule opens into the epididymis below 

 the globus major; the inferior opens at the globus minor; both lie between 

 the testis and the epididymis. They are lined with a single layer of colum- 

 nar epithelium, sometimes ciliated. The inferior ductule is the more gen- 

 erally present, and has a length of about five centimeters. 



The PARADIDYMIS (organ of Giraldes) lies within the spermatic cord 

 between the head of the epididymis and the pampiniform plexus. It con- 

 sists of a variable number of irregular branching tubules, blind at both 

 ends, and lined with a single layer of columnar, ciliated epithelium. These 

 tubules also represent persisting rudimentary mesonephric tubules. 



The SINUS POCULARIS (sinus prostaticus) represents the remnant of the 

 proximally fused degenerated fetal Miillerian ducts. It is the homologue of 

 the vagina in the female. It is a shallow, blind pocket opening into the 

 floor of the prostatic portion of the urethra ; it may be bifid distally, varies 

 in length from six to twelve millimeters, and is lined with a columnar 

 epithelium which may be locally ciliated. 



