CHAP, i.l MALE ORGANS. 373 



that gland into the urethral canal. So far plain muscular fibres 

 only are brought into play ; but the act is completed by the aid of 

 striated muscles, namely, by forcible contractions of the levator 

 ani, of the constrictor urethra including the external sphincter of 

 Henle, of the ischio-cavernous muscle, which starting from_the 

 ischium on each side embraces the root of the penis, and of the 

 bulbo-cavernosus muscle (or ejaculator urime) which starting from 

 the perinaeum embraces the beginning of the urethra and corpus 

 spongiosum. A contraction begins in the external sphincter ani, 

 extends to the levator ani and then passes to the other muscles, 

 progressing in a wave-like manner from behind forwards, and is 

 repeated in a more or less distinctly rhythmic manner until all the 

 semen is ejected from the urethra. 



These expulsive contractions, especially the last named, appear 

 like erection to be carried out by the help of a centre in the 

 lumbar region of the cord, and for them afferent impulses 

 generated in the sensitive surface of the glans penis are more 

 essential than for simple erection. In the dog stimulation of the 

 internal pudic nerve throws the whole group of striated muscles 

 just named into successive contractions as described, but each 

 muscle may be made to contract separately by stimulation of its 

 own individual branch. 



The semen being received into the vagina, the walls of which, 

 and especially the external appendages of which, are at the time in a 

 state of turgescence resembling the erection of the penis, but less 

 marked, lies, probably, at the far end of the vagina in a pool into 

 which the os uteri dips ; and it is possible that contractions of the 

 round ligaments (which contain striated muscular fibres) by tilting 

 the cervix backwards assist in bringing the os uteri into the semen. 

 In this manner the spermatozoa find their way into the uterus and 

 so into the Fallopian tube, where (probably in its upper part) they 

 come in contact with the ovum. In the rabbit spermatozoa may 

 reach the ovary within two hours after coitus. In the case of some 

 animals impregnation may take place at the ovary itself. The 

 passage of the spermatozoa is most probably effected mainly by 

 their own vibratile activity ; but in some animals a retrograde 

 peristaltic movement travelling from the uterus along the Fallopian 

 tubes has been observed ; this might assist in bringing the semen 

 to the ovum, but inasmuch as these movements are probably parts 

 of the act of coitus and impregnation may be deferred till some 

 time after that event, no great stress can be laid upon them. 



