230 MAMMALIA. 



FIG. III. 



(THE SAME.) 



IT shows the ganglion of the aortic plexus, and the hypogastric plexus of each 

 side, of the natural size. 



The spermatic nerves do no more than excite, and then maintain, a proper action 

 in the ovary and its bloodvessels, for the growth of the ova, as the fecundation of 

 these, in many instances, takes place after their exclusion. 



The distribution of branches of the sympathetic nerve only to the ovary and upper 

 part of the uterus of an uniparous animal, and to nearly the whole of the long horn of 

 a multiparous one, makes it probable that these are necessary for the growth of this 

 organ and the embryo, and that the conjoined hypogastric and sacral nerves more 

 especially determine the first changes required for parturition. Whether the animal 

 be uniparous or multiparous, or the neck of the uterus be placed high up or low down, 

 the conjoined hypogastric and sacral nerves are directed most to the lower part of the 

 uterus and the vagina, and render these parts more irritable than if they had been 

 furnished by the sympathetic only, so that near the maturity of the embryo the exten- 

 sion and pressure gradually excite the more sentient nerves ; from these the irritation 

 is conveyed to the other uterine nerves, and produces the tetanic expulsive action : the 

 disposition of the nerves of a multiparous animal leads to the conclusion that the 

 parturient action commences from below in the part containing the lowest foetus. The 

 particular arrangement of the nerves and bloodvessels, by allowing a slower or more 

 free circulation in the uterus and foetus, has some share in determining the period of 

 birth ; in the multiparous animal it permits a more rapid growth of the foetuses, as 

 each, with the portion of uterus containing it, is supplied with blood equally and freely 

 throughout ; in the uniparous the supply of blood is more limited, the arteries and 

 nerves becoming more influenced in succession according to the required progress of 

 enlargement of the uterus and foetus. 



