262 HISTOLOGY. 



The epithelium of the mucosa is two-layered in the distended bladder, the 

 outer cell having terminal bars; in the contracted condition it becomes 

 several-layered and the bars from a net extending into the epithelium. 

 Some of the superficial cells have a cuticular border; they often contain 

 two nuclei and their darkly granular protoplasm has been considered 

 suggestive of secretory activity. Round or oval pockets extend into the 

 tunica propria (Fig. 297). Some have no lumen or are detached from 

 the epithelium, but others are pits containing a colloid substance. The 

 pits are the first stages of gland formation. In the adult, branched tubules 

 lined with cylindrical epithelium may sprout from the bottom of the pits, 

 thus forming true glands. Their occurrence is limited to the fundus (the 

 dorsally bulging lower part of the bladder) and to the neighborhood of 

 the urethral outlet. In the latter position they present transitions to well 

 developed prostatic glands. 



The tunica propria sometimes contains solitary nodules. It blends 

 with the submucosa, as in the ureter, and contains lymphatic and blood 

 vessels, the latter extending very close to the epithelium. 



The muscularis consists of smooth muscle fibers arranged in three 

 interwoven layers, which are seldom separable in sections. They 'are an 

 inner longitudinal, middle circular and outer longitudinal layer. The 

 circular fibers are strengthened at the beginning of the urethra to form 

 the "internal sphincter" of the bladder, a muscle not always distinct. 



The serosa is a connective tissue layer covered with mesothelium. 

 In the non-peritonaeal part of the bladder it is replaced by an adventitia 

 or fibrous layer. 



Non-medullated nerves, with scattered groups of ganglion cells, are 

 found outside of and among the muscles. Medullated fibers terminate 

 around the ganglion cells; others pass through the ganglia to intra-epi- 

 thelial sensory endings. 



URETHRA (IN THE FEMALE). 



The male urethra will be described with the genital organs; only its 

 upper portion is homologous with the urethra of the female which is 

 exclusively the outlet of the urinary tract. The epithelium has been 

 variously described as stratified, with outer squamous cells, or as pseudo- 

 stratified, and columnar. It may be of different form in different indi- 

 viduals. The lumen is irregularly crescentic with longitudinal folds, as 

 seen in Fig. 298. Branched tubular urethral glands are found only in 

 small numbers except near the outlet. Their secretion is mucoid, but is 

 not typical mucus. In the submucosa there are many thin walled veins 

 constituting the corpus spongiosum. It is comparable with the upper 



