THE HUMAN PROSTATE GLAND 309 



of the urethra and its surrounding tissue. Under the main por- 

 tion of the middle lobe thelumina of the vasa deferentia spread out 

 laterally as shown in fig. 2 and form a lateral branch or bending 

 which marks the first appearance of the seminal vesicles. Im- 

 mediately below this point at the beginning of the ejaculatory 

 ducts, the lumina constrict, and the surrounding tissue is less 

 abundant. The structures surrounding the ejaculatory ducts 

 which have to this point remained separate now intermingle with 

 the muscular walls of the urethra and firmly bind the two struc- 

 tures together. 



At this point the utriculus prostaticus which has been very 

 small begins to enlarge and finally becomes larger than the two 

 ejaculatory ducts which decrease in size as they approach the ure- 

 thral lumen. 



In the progress of the two ejaculatory ducts and utriculus pros- 

 taticus toward the lumen of the urethra, the tissues surrounding 

 the two structures are closely bound together, but the mass of 

 tissue around the ejaculatory ducts and utriculus prostaticus 

 maintains its identity and by its further progress pushes the flat- 

 tened floor of the urethra up into a mound-like projection trans- 

 forming its triangular lumen into an inverted semilunar shaped 

 structure and forming the verum montanum, the main tissue of 

 which is thus derived from the walls of the ejaculatory ducts. 



Fetus 8 cm. long: {thirteen weeks. No. 54- in Dr. Mall's collection) 



This fetus shows exactly the same distribution of elements as 

 the one just described. The number of tubules is reduced, prob- 

 ably due to the fact that the sections were three times as thick as 

 the ones discussed above and this might have obscured some of 

 them. 



The middle lobe region gives rise to seven glands. Twenty- 

 seven tubules are found in the two prostatic furrows which will 

 form the lateral lobes and six others are located on the floor of the 

 urethra caudalward from the entrance of the ejaculatory ducts 

 which represent the posterior lobe of the prostate. These latter 

 send branches caudalward or anteriorly as well as cranialward or 



