1118 ACCESSORY MALE ORGANS. [BOOK iv. 



contractions of the levator ani, of the constrictor urethrae 

 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 urinse) which starting from the perinseum 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 bring- 

 ing the os uteri into the semen. In this manner the spermato- 

 zoa 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 bring- 

 ing 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. 



