336 OSWALD S. LOWSLEY 



birth some of the tubules are surrounded by very dense muscular 

 layers. 



In every case but one in this study the middle lobe of the pros- 

 tate develops independently from tubules which originate from 

 the floor of the urethra near the middle line between the bladder 

 and the entrance of the ejaculatory ducts. The tubules compos- 

 ing this lobe are separated from the lateral lobes by a considerable 

 area of tissue free from glandular elements, the younger the em- 

 bryo the greater the separation. In later development while the 

 tubules and their branches maintain their characteristic position, 

 there does not seem to be any definite formation of a fibrous cap- 

 sule separating the middle from the lateral lobes. The ducts of 

 the largest of the middle lobe tubules which were originally near 

 the middle line are pushed laterally by the further development 

 of the structures in the verum montanum so that they open 

 rather high up on its sides and not in the middle line, as that part 

 is occupied by the utriculus prostaticus and the ejaculatory ducts. 

 Rarely (once in our experience) there may be an absence of inde- 

 pendent middle lobe tubules, in which case branches from the 

 lateral lobes are seen approaching the middle line in the region- 

 ordinarily occupied by the middle lobe, and if the growth con- 

 tinues this region will be occupied by a glandular commissure such 

 as Jores declares all middle lobes to be. In most cases the middle 

 lobe is made up of nine or ten large tubules, the number in five 

 cases varying from seven to twelve, the average being ten. 



As one of our embryonic series showed an absence of tubules 

 in the middle lobe region it was deemed advisable to determine 

 the percentage of prostates that have a middle lobe. 



Dissecting room and autopsy subjects to the number of twenty 

 were examined and all demonstrated definite prostatic tissue in 

 the middle lobe region. Ten sets of serial sections of embryonic 

 tissue demonstrated only one case without independent middle 

 lobe tubules. Thirty-three autopsy cases of enlarged prostate 

 in the Johns Hopkins Hospital Genito-Urinary Museum were 

 examined, with the result that in thirty-one, definite middle lobes 

 were identified. The existence of middle lobes in the other two 

 cases could not be determined, as the specimens were not sec- 



