ON GENERATION. 487 



sions to its mother's sides : the whole can most readily be 

 withdrawn from the uterus, as I have ascertained with an ovum 

 which contained a foetus nearly the length of the thumb. It 

 is manifest, therefore, that the foetus up to this period has been 

 nourished by the albumen alone that is contained within the con- 

 ception ; in the same way as we have ascertained the process to 

 go on within the hen's egg. The mouths of the umbilical veins 

 are lost and obliterated between the albumen and neighbouring 

 humours of the conception and their containing membranes ; 

 but nowhere is there as yet any connexion with the uterus, 

 although by these veins alone is nourishment supplied to the 

 embryo. And as in the egg the ramifications of the veins are 

 first sent to the colliquament, (in the same way as the roots of 

 trees penetrate the ground,) and afterwards take their course to 

 the external tunic called the chorion, whereon, for the sake of 

 the nourishment, they are dispersed in an infinity of ramifica- 

 tions through the albuminous fluid contained within the outer 

 membrane, so have I observed veins in the chorion of a human 

 abortion ; and Aristotle l also states " that membrane to be 

 crowded with veins." 



If the foetus be single its umbilical vessels are distributed to 

 both horns, and a few twigs are also sent to the intervening 

 body of the uterus ; but if the conception be double, one in 

 either horn, each sends its umbilical vessels to its own horn 

 alone; the embryo in the right horn deriving nourishment 

 from the right part of the conception, that in the left from the 

 left portion of the same. In other respects the twin-concep- 

 tion here is precisely similar to the twin-conception of the egg. 



Towards the end of November, then, all the parts are clearly 

 and distinctly to be distinguished, and the foetus is now of the 

 size of a large bean or nutmeg ; its occiput is prominent, as in 

 the chick, but its eyes are smaller ; the mouth extends from 

 ear to ear, the cheeks and lips, as consisting of membranous 

 parts, being perfected at a very late period. In the foetuses of 

 all animals, indeed, that of man inclusive, the oral aperture 

 without lips or cheeks is seen stretching from ear to ear ; and 

 this is the reason, unless I much mistake, why so many are born 

 with the upper lip divided as it is in the hare and camel, whence 



1 Hist. Anim. lib. vii. cap. 7. 



