CALLITHRIX JACCHUS, THE MARMOSET 157 



Forebrain index 80 . 5 per cent 



Midbrain index 0.5 per cent 



Hindbrain index 19.0 per cent 



Courtesy. American Museum oj Natural History 



FIGS. 71 AND 72. HAND AND FOOT OF MARMOSET. 



Left. Dorsum of hand showing poorly developed thumb, and claws instead of finger-nails. 

 Right. Dorsum of foot showing rudimentary toe, claws instead of toe-nails. 



These indices align the animal in a definitely submanual group with a 

 forebrain index slightly below that of the lemur and only slightly above the 

 forebrain index characteristic of mammals possessed of paws and claws. 



SuRF.\CE Appearance of the Brain in Callithrix Jacchus 



THE FISSURAL PATTERN 



The surface appearance of the hemisphere in the marmoset gives the 

 impression at first glance of a lissencephalic brain. Further inspection, how- 

 ever, shows that at least three fissures constitute an indefinite lissural pattern 



