URINARY PASSAGES. 223 



(b) Urethra. 



(1) Male. The urethra consists of a mucosa, submucosa, and 

 muscularis, somewhat differently arranged in the different 

 regions of the canal. In the pars prostatica the epithelium is 

 quite similar to that of the bladder ; in the pars membranacea 

 there is a stratified cylindrical epithelium, which in the pars 

 cavernosa is converted into two rows of cylindrical cells. The 

 last segment, the fossa navicularis, is lined with flat stratified 

 epithelium. 



The tunica propria contains numerous elastic fibres and 

 forms papillae in close contact with the epithelium. These are 

 developed most strongly in the fossa navicularis. The sub- 

 mucosa contains a rich plexus of veins, and in the whole canal 

 there are here present branched tubular glands glandular 

 (irethrales (Littre) which are more numerous in the posterior 

 part. They are lined with cylindrical glandular epithelium 

 and extend into the submucosa. 



The muscularis in the prostatic and membranous urethra 

 shows two layers of smooth muscle fibres, an inner longi- 

 tudinal, and an outer circular coat. The circular coat is want- 

 ing in the pars cavernosa, arid the longitudinal layer becomes 

 very thin. 



The whole urethra is highly vascularized (see Corpus cav- 

 er nosum urethrse). The nerves form networks of fibres, 

 which end freely or in various end organs (see Nerve-endings). 



(2) Female. In the female the urethra is considerably 

 shorter and not so definitely divided into sections. We can 

 distinguish a wall made up of the same layers as in the male. 

 The epithelium in the upper part is like that of the bladder, 

 but lower down becomes a single or double layer of columnar 

 cells, and finally passes over at the lower end into a stratified 

 pavement epithelium. 



The tunica propria forms papillae at its junction with the 

 epithelium. These are highest in the region of the urethral 

 opening. Littre's urethral glands are present here also, but are 

 not so numerous as in the male. The muscularis consists of an 

 inner longitudinal and an outer circular coat of smooth muscle 



