XIl] THE MALE GENERATIVE ORGANS 150 



process. As is sho\^n below there is evidence that the function of 

 the filiform process is insertion into the month of the uterus^. 



In the bnll the lihform appendage is represented bj^ a vestigial 

 structure or jjajjilla which is situated on the left side of the penis 

 in the same jjosition as the appendage in the ram, only in the bull 

 the process does not project beyond the end of the organ. When 

 erected the bull's penis does not increase in diameter to the same 

 extent as in the horse owing a^oparently to the thickness of the 

 jorepucial folds. 



The penis in the boar like that of the horse is not provided 

 with a filiform prolongation or lateral j^apilla, and the urethral 

 aperture is situated at the end of the organ and in the centre. 



Erection, Ejaculation and Coition. The erection of the penis is 

 brought about mainly b}' the dilatation of its vessels. First of all 

 the proximal portion of the organ increases in size, and then the 

 swelling extends throughout the corpora cavernosa, and eventually 

 to the glans. The arterial jDressure in the penis dimng erection has 

 been found to rise from about one-half to three-fifths of that of 

 the carotid. The erection is effected parti}- by the contraction of 

 the ischio-cavernosus (or erector jDcnis) and bulbo-cavernosus 

 nuiscles which arrest the flow of blood along the efferent vessels, 

 but it is believed also that the unstriated muscle fibres which are 

 scattered through the framework of the corjDora participate in the 

 process. According to Kolliker the action of these muscles is 

 temporarily inhibited and the trabecular framework of the cor- 

 pora is correspondingly relaxed. The Avhole jirocess, which is 

 essentially a reflex action, is presided over by a centre situated in 

 the lumbo-sacral part of the spinal cord, and Eckhard and others 

 have shown that the efferent nerves (called the nervi erigentes) 

 arise from the 1st, 2nd and 3rd sacral nerves and are vaso-dilator 

 in function. On stimulating the uervi erigentes electrically the 

 penis can be made to erect. 



Seminal ejaculation is brought about by a series of muscular 

 contractions, Avhich begin in the walls of the vasa eft'erentia and 

 pass to the ejjididymis and thence along the vas deferens on either 

 side. The vesiculae serainales contract simultaneously and the 

 prostatic muscles also contract. The internal generative organs 

 are supplied by nerves coming from the lumbar region, and 

 Langley and Anderson found that stimulation of these nerves in 



^ For description of the uterus and other female organs, see next chapter. 



