Corpus Spongiosum and the Corpus Cavemosum. 25 



have to be ascertained whether certain epithelial cells of the urethral 

 mucous membrane are real terminations of nerves, and others real 

 terminations of muscular fibres. If we consider the extreme sensi- 

 tiveness of the epithelial layer of the healthy cornea to the contact of 

 ever so fine a foreign body ; if we consider that the most superficial 

 contact of the point of a needle with the cornea produces the most 

 severe pain and reflex movements ; while, after destruction of the 

 most superficial layer at one point, the needle produces at that point 

 only an inconsiderable amount of pain — facts which every physician 

 has opportunity to observe in removing foreign bodies (dust, iron 

 filings, particles of coal, &c.) from the cornea — the conclusion is 

 almost irresistible that the epithelial covering of the cornea consists 

 of cells which are to be regarded as nerve terminations. 



Physiologij. — The cause and mechanism of erection may be 

 said to depend upon two phenomena occurring simultaneously : — 



1. Upon an increased influx of blood through the arteries which 

 empty by the arterial helicinae into the venous cavities. 



2. Upon mechanical pressure affecting the veins which convey 

 the blood from the penis, whereby a retardation of the venous cir- 

 culation is induced. 



In the passive condition of the penis the same quantity of blood 

 flows to and from the organ, but during erection the entire arterial 

 system becomes distended, especially those known as the arterise 

 helicinae become actively dilated, and empty themselves into the 

 venous cavities. The dilatation of these vessels is supposed to be 

 effected through the agency of the special system of longitudinal 

 bundles of muscles which accompany, and whose fibres are inserted 

 into the walls of these arteries. 



The muscles chiefly concerned in arresting the efflux of blood, 

 or at least preventing it from being as great as the influx, are the 

 acceleratores urinae and erectores penis. 



The contraction of the acceleratores urinae muscles impedes the 

 return of blood through the vena corporis spongiosi, by pressure 

 upon the bulbous portion of the corpus spongiosum. 



The erectores penis act as erectors, by compressing the crura 

 and vena dorsalis. They embrace the root of the penis and com- 

 press it. The pressure upon the vena dorsalis impedes the return 

 of blood by this vessel, and the pressure upon the crura produces 

 the same effect upon the veins of the corpus cavernosum. 



The transversus perinei probably assists the posterior fasciculi 

 of the acceleratores urinae in producing turgescence of the corpus 

 spongiosum, by virtue of its insertion into the fibrous tunic of the 

 bulb. 



These muscles are supplied with nerves by the pudic branch of 

 the sacral plexus, and it is an interesting fact, capable of demonstra- 

 tion upon the lower animals, that after division of this nerve the 

 penis is incapable of erection. 



