STRUCTURE OF THE COLLICULUS SEMINALIS. 301 



is also the character of the epithelium of the lower wall of the 

 urethra. The thickness of this layer is considerably greater at 

 the base than at the apex of the colliculus. In the former 

 situation it amounts to 0*31 of a millimeter, but in the latter 

 it does not exceed a third of this thickness. At the base large 

 conical papillae, somewhat dilated at their extremities, and con- 

 taining vessels, project into the epithelium, but towards the 

 apex they become progressively smaller, till at the apex itself 

 they are no longer perceptible. The vesicula prostatica is also 

 lined by a laminated pavement epithelium into which small 

 conical papillae project. Both upon the colliculus and in the 

 vesicula, short-branched and tortuous glands open, into which 

 the laminated pavement epithelium is prolonged. 



The vesicula prostatica is surrounded by a small quantity of 

 vascular connective tissue, and by numerous muscular fibres. 

 The latter are in direct connection with the smooth muscular 

 fibres that extend upwards from the deeper portion of the 

 prostate, as well as with those that are found in the wall of 

 the ductus ejaculatorii. In general it may be said that the 

 fasciculi in immediate contiguity to the vesicula prostatica 

 decussate obliquely with one another. To these oblique fibres 

 there succeeds a circular layer, which may be regarded as the 

 direct prolongation of the external circular muscular layer of 

 the ductus ejaculatorii. This circular layer investing the 

 vesicula prostatica is most feebly developed in the neighbour- 

 hood of the epithelium of the colliculus seminalis. 



VI. URETHRA. The epithelium of the urethra, along the 

 lower wall of the root of the pars prostatica and membranacea, 

 is a laminated pavement epithelium ; at the sides and upon 

 the upper wall of these parts it is in great part a laminated 

 transitional epithelium, in which are ^a few small islands of 

 laminated pavement epithelium. 



This transitional epithelium, however, is so far peculiar that 

 the middle cells are clavate, whilst the upper are partly tesse- 

 lated and partly clavate. The thickness of the epithelium 

 varies from 0'09 to O'l of a millimeter, and it is somewhat 

 thinner on the upper wall than upon the lower. 



The mucous membrane has an average thickness of 0'36 to 



