STRUCTURE OF THE URETHRA. 303 



In the lower wall the circular layer consists only of small fasci- 

 culi, separated from each other by a considerable quantity of con- 

 nective tissue, and in the child has a thickness varying from 1*3 

 to 1'6 of a millimeter. The external layer is somewhat thinner, 

 being composed of smaller fasciculi. The two layers are con- 

 nected with one another by oblique and decussating fasciculi. 



Towards the upper wall of this portion of the urethra the 

 two layers become somewhat more continuous, the fasciculi 

 of each being larger and more closely approximated. Through- 

 out the whole periphery of the tube, however, small fasciculi 

 enter the mucous layer obliquely, and break up into isolated 

 fibres which may be followed to the epithelium. 



In the pars prostatica the musculature of the urethra is inti- 

 mately connected with that of the prostate, the fasciculi of 

 which, composed of unstriated fibres, are recognizable, running 

 for the most part longitudinally immediately beneath the 

 mucous membrane. 



In the pars membranacea a continuous layer of longitudinal 

 muscular fibres, having a thickness of 0*58 of a millimeter, is 

 alone distinguishable immediately beneath the mucous mem- 

 brane, and from this numerous fasciculi are given off obliquely, 

 which enter the mucous membrane. The large vascular and 

 nervous trunks lie on the outer side of the muscular tunic, 

 and the arteries, after having distributed numerous branches 

 to this tunic, enter the mucous membrane, where they give off 

 single and double capillary loops to the papillae, and are then 

 continuous with the subepithelial venous rootlets. These, 

 rapidly increasing in size, and intercommunicating by numerous 

 anastomoses, form a venous plexus belonging to the mucous 

 membrane, the meshes of which have a predominating longi- 

 tudinal direction. 



Between these large veins muscular bands from the muscular 

 tunic extend into the mucous membrane. The thickness of 

 this venous plexus gradually increases towards the anterior 

 extremity of the pars membranacea. 



In their course outwards these veins decrease again in 

 number and size, or, in other words, from this venous plexus 

 smaller veins run outwards, which receive, as they perforate 

 it, the veins of the muscular tunic. 



