148 PHYSIOLOGY CHAP. 



were dominated by two distinct nervous impulses which alternate 

 and follow one another rhythmically, this ingenious theory would 

 find an experimental basis. 



In any case one must reject the old opinion first expressed by 

 E. H. Weber in 1836, which ascribed to the colliculus seminalis 

 (called also the caput gallinaginis and veru montanum) the office 

 of closing the urethral canal and making micturition difficult or 

 impossible during erection. 



The colliculus has not the structure of an erectile organ, and 

 for this reason is incapable of occluding the urethra ; on the other 



FIG. 40. Superficial muscles of the perineum in the male. (Chiarugi.) 1, ischio-cavernosus 

 muscle ; 2, bulbo-cavernosus muscle ; 2', constrictor radicis penis of the bulbus cavernosus 

 which forms the loop of Houston ; 3, transverse superficial muscle of perineum ; 4, external 

 sphincter of anus ; 5, urogenital trigone, inferior surface ; ti, bulbo-urethral gland ; 7, tendinous 

 centre of perineum ; 8, levator ani ; 9, gluteus maximus. 



hand, if the colliculus through the effect of muscular contractions 

 could obstruct the urethral canal, at the same time would be 

 occluded the orifices which admit into it the secretions of the 

 testicle and prostate ; and thus as Walker justly notes their 

 ejaculation externally would be prevented. 



The expulsive action of the smooth muscle of the urethra 

 is helped greatly by the reflex or voluntary contraction of the 

 external striated sphincter of Henle, the bulbo-cavernosus muscle 

 which embraces the bulbar portion of the corpus spongiosum, 

 and the ischio-cavernosus muscle which surrounds the roots of 

 the corpora cavernosa of the penis (Fig. 40). The contraction 

 of these muscles is repeated in a more or less distinctly 



