NORMAL HISTOLOGY. 



urethral crest, the fusiform ridge modelling the posterior wall of the prostatic 

 portion of the canal, the mucous membrane acquires the character of erectile 

 tissue on account of the abundance of the venous channels occupying the 

 deeper layer of the tunica propria. 



The muscular tissue associated with the male urethra includes in- 

 trinsic and extrinsic fibres, the former being involuntary and directly incor- 

 porated with the wall of the canal and the latter being accessory strands of 

 striped muscle derived from structures surrounding the urethra. The in- 

 trinsic muscle is arranged as an inner longitudinal and an outer circular 

 layer, of which the longitudinal is thinner but more widely distributed, 

 extending from the internal urethral orifice at the bladder as far forwards 

 as the openings of the bulbo-urethral glands in the pars cavernosa. The 

 circular fibres, outside the longitudinal ones, are best developed at the 

 internal urethral orifice, where they are three or four times as thick as those 

 running lengthwise. They gradually diminish and just beyond the mern- 



Surface epithelium 



Intramucosal glands 



Blood- 

 vessels 



FIG. 270. Section of mucous membrane of prostatic urethra, showing gland-like crypts in mucosa. X 45. 



branous urethra disappear, first on the lower and last on the upper wall of 

 the dilatation, the fossa bulbi. In advance of the posterior third of the 

 spongy portion, the intrinsic muscle is wanting, the unstriped muscular 

 tissue surrounding the remainder of the canal belonging to the erectile tissue 

 of the corpus spongiosum which the urethra traverses. The internal vesical 

 sphincter, encircling the commencement of the urethra, is derived from the 

 muscular sheet of the trigonum of the bladder. At the apex of the prostate 

 gland, the urethra is surrounded by bundles of striped muscle, known as the 

 external vesical sphincter, prolonged upwards from the compressor urethrse 

 muscle. 



The urethral glands, or glands of Littre, embrace two groups, those 

 within the mucous membrane and those immediately outside, whose ducts 

 are seen with a magnifying glass as minute openings on the mucous surface. 

 The former, the intramucosal glands, are small and simple, consisting usually 

 of a single alveolus, less frequently of two or three. They are lined with 

 columnar epithelium and occur in all parts of the urethra, but are most 

 numerous in the spongy portion. The extramucosal glands, although small, 

 are larger than the preceding but less widely distributed, since they are 

 absent in the distal half of the membranous and the proximal third of the 



