348 THE ORGANS 



The Seminal Vesicles and Ejaculatory Ducts. — The seminal 

 vesicles. The walls of the seminal vesicles are similar in structure to 

 those of the ampulla. The epithelium is pseudo-stratified with two 

 or three rows of nuclei and contains a yellow pigment. When the 

 vesicles are distended the epithelium flattens out and the nuclei lie 

 more in one plane, thus giving the appearance of an ordinary simple 

 columnar epithelium. Beneath the epithelium is a thin stroma, out- 

 side of which is an inner circular and an outer longitudinal layer of 

 smooth muscle, both layers being much less developed than in the 

 vas. The seminal vesicles are to be regarded as accessory genital 

 glands. 



The ejaculatory ducts are lined with a single layer of columnar 

 cells. The muscularis is the same as in the ampulla except that the 

 inner circular layer is thinner. In the prostatic portion of the duct 

 the muscularis is indistinct, merging with the muscle tissue of the 

 gland. The ducts empty either directly into the urethra or into the 

 urethra through the vesicula prostatica. 



Rudimentary Structures Connected with the Development of the Genital 

 System. — Connected with the testicle and its ducts are remains of certain 

 foetal structures. These are: 



(i) The paradidymis, or organ of Giraldcs, situated between the vessels of 

 the spermatic cord near the testis. It consists of several blind tubules lined 

 with simple columnar ciliated epithelium. 



(2) The ductus aberrans Halleri, found in the epididymis. It is lined with 

 simple columnar ciliated epithelium and opens into the vas epididymis. In- 

 stead of a single ductus aberrans, several ducts may be present. 



(3) The appendix testis (stalked hydatid or hydatid of INIorgagni), in the 

 upper part of the globus major. It consists of a vascular connective tissue 

 surrounding a cavity lined with simple columnar ciliated epithelium. 



(4) The appendix epididymidis, a vascular structure, not always present, 

 lying near the appendix testis. It resembles the latter in structure. 



The paradidymis and ductus aberrans Halleri probably represent remains 

 of the embryonal mesonephros. The appendix testis and the appendix epididy- 

 midis are believed by some to be derived from the primitive kidney, by others 

 from the embryonal duct of Miiller. 



Blood-vessels. — Branches of the spermatic artery ramify in the 

 mediastinum and in the tunica vasculosa. These send branches into 

 the septa of the testicle, which give rise to a capillary network among 

 the convoluted tubules. From the capillaries arise veins which 

 accompany the arteries. 



Lymph capillaries begin as clefts in the tunica albuginca and in 

 the connective tissue surrounding the seminiferous tubules. These 



