MAN. 333 



vein, with which is connected ;i hemi-ozygos vein developed from 

 part of the left posterior cardinal. 



The inferior vena cava (posterior v.c.) only becomes important 

 when the hind-limbs have been developed to some extent. It is 

 formed by the union of iliac veins. 



5. Urinogenital System. The excretory organs of the embryo 

 consist, as in the rabbit, of a mesonephros (Wolffian body) on 

 each side, from which a mesonephric duct (Wolffian duct) runs 

 back to open into an urinogenital sinus. The adult kidney is a 

 metanephros, and the ureter (metauephric duct) is an outgrowth 

 from the posterior end of the mesonephric duct. As before, the 

 bladder is the proximal end of the allantois. The reproductive 

 organs at first consist of a pair of gonads and two Mullerian ducts, 

 and later on the excretory organs of the embryo in part become 

 genital ducts, and in part are reduced to rudiments, which are of 

 considerable importance from a medical point of view, since they 

 may enlarge and become the seat of disease. The following table 

 exhibits the most important details regarding the fate of the 

 embryonic excretory organs and Mullerian ducts. Rudiments are 

 italicized. 



As compared with the Rabbit it should be noticed that (1) in 

 the male there are vesicuhie seminales, while the uterus masculinus 

 is relatively small. (2) In the female the most important part is 

 the single uterus, though in abnormal cases the Mullerian ducts 

 may fuse less completely. 



6. Nervous System. The brain (Figs. 106 and 1 07) is exceed- 

 ingly large, one result of which is to profoundly influence the 

 shape and proportions of the skull, as already explained. This 

 increased size is mainly due to the enormously developed cerebral 

 hemispheres, which overlap and largely conceal the other regions, 

 extending in all directions to such an extent that nothing else is 

 visible in a brain viewed from above. In the rabbit the hemi- 

 spheres leave the cerebellum quite uncovered, while they are 

 nearly smooth and a division into lobes is only indicated. In 

 each hemisphere of the human brain, on the contrary, six chief 

 lobes can be distinguished, and its surface is marked by elabor- 

 ately arranged convolutions (gyri) separated from one another by 

 furrows (sulci). In this way the surface is 5| times as great as 

 if it were smooth, and the extent of the cortex is correspondingly 

 increased. It is an established fact that the intelligence of an 



