306 EXTERNAL GENERATIVE ORGANS, BY E. KLEIN. 



of those muscular fibres to which reference has already been 

 made. 



Near the bulb the whole of the lower and a great part of 

 the lateral portion of the urethral mucous membrane is lined 

 by a laminated pavement epithelium 0'18 of a millimeter in 

 thickness. This layer resembles that of the oral cavity and of 

 other parts, except that the uppermost cells do not appear to 

 be so strongly flattened, whilst some contain an oblong and 

 others a more rounded nucleus. The cells of the deepest layers 

 are rounded or polyhedric, with spheroidal and relatively large 

 nuclei. Proceeding from the bulb, the surface lined by this 

 laminated pavement epithelium gradually diminishes in extent, 

 being found only for a short distance along the median line of 

 the lower surface of the urethra, where it is replaced at first 

 by laminated transitional and subsequently by columnar epi- 

 thelium. This replacement occurs earlier at the sides, and still 

 sooner on the upper surface. 



Variations, however, occur in this respect ; islands of 

 laminated pavement epithelium not unfrequently occurring in 

 newly born children, both on the upper and lower surfaces of 

 the urethra, in the body of the penis. The columnar epithelium 

 with which the urethra is lined to near the fossa navicularis 

 presents columnar cells in the most superficial tiers, whilst 

 those composing the middle and deeper layers are clavate or 

 fusiform. At certain points there is only a single layer of 

 columnar cells. As the lumen of the urethra begins to be 

 elongated vertically from above downwards, its whole surface 

 is invested with laminated pavement epithelium, which how- 

 ever forms a jnuch thicker layer on the lower than upon the 

 upper surface. The epithelium of the upper half is further 

 distinguished from that of the lower by its superficial cells 

 being more flattened and coalesced with one another. The 

 deepest layer of the epithelium, both on the upper and lower 

 part, consists of short columnar cells with rounded nuclei, 

 arranged in a palisade-like manner. 



The mucous membrane of the urethra everywhere presents 

 longitudinal folds, which are joined at certain points by trans- 

 verse membranous processes forming the lacunae of Morgagni. 



The thickness of the mucous membrane varies considerably 



