STRUCTURE OF THE URETER 



201 



The mucous membrane is composed of areolar tissue and is lined by 

 transitional epithelium. 



The urinary bladder has a muscular wall lined by a strong mucous 

 membrane and covered in part by a serous coat. 



The muscular coat consists of three layers, but the innermost is 

 incomplete. The principal fibres run longitudinally and circularly, 

 and the circular fibres are collected into a layer of some thickness 

 which immediately surrounds the commencement of the urethra, form- 

 ing the sphincter vesicce. The mucous membrane is lined by a transitional 

 stratified epithelium like that of the ureter. The shape and structure 

 of the cells have already been studied (Lesson VII.). 



The nerves to the bladder form gangliated plexuses, and are dis- 

 tributed mainly to the muscular tissue and blood-vessels, but some are 

 said to enter the epithelium. 



FIG. 235. SECTION OP ERECTILE TISSUE. (Cadiat.) 



a, trabeculse of connective tissue, with elastic fibres, and bundles of plain muscular 

 tissue (c) ; 6, venous spaces. 



The penis is mainly composed of cavernous tissue which is collected 

 into two principal tracts the corpora cavernosa, one on each side, and 

 the corpus spongiosum in the middle line inferiorly. All these are 

 bounded by a strong capsule of fibrous and plain muscular tissue, 

 containing also many elastic fibres and sending in strong septa or 

 trabeculse of the same tissues, w^hich form the boundaries of the caver- 

 nous spaces of the erectile tissue (fig. 235). The arteries of the tissue 

 run in these trabeculse, and their capillaries open into the cavernous 

 spaces. On the other hand, the spaces are connected with efferent 



