Cortical Lamination, etc., in Brain of Marmoset. 125 



in the preservation of the animal, consequently the olfactory nerves and the 

 archicortex are relatively less developed, but the occipital cortex is more 

 developed, and forms a definite occipital lobe covering the cerebellum. 

 The relative extent of the motor area and tactile motor or kintesthetic area 

 of the neo-cortex of the Marmoset, compared respectively with that of the 

 Lemur and with that of the Macacus rhesus, shows that it corresponds more 

 with the former than with the latter. This fact may be correlated with 

 the following statement by Bates concerning the habits of the Marmoset : 

 " they are arboreal animals, but their manner of climbing resembles that 

 of squirrels rather than monkeys ; this is due to the fact that they have 

 no means of gripping a bough since the poUex is not opposable, neither is 

 the tail prehensile. They therefore confine themselves to the larger 

 branches, where their long claws are of assistance in enabling them to cling 

 securely to the bark." The Marmosets, owing to their claws and non- 

 opposable pollex, are unable to use their limbs for prehension with anything 

 like the delicacy and refinement of the higher Apes. Although the 

 Marmoset possesses stereoscopic vision, it is unable to translate all visual 

 into tactile-motor impressions to the same degree of perfection as the 

 Macacus, consequently the stereognostic sense must be comparatively 

 rudimentary. This fact may account for the existence of a convoluted 

 parietal lobe which indicates a considerable extension of surface lying 

 between the occipital lobe and the post-central convolutions in the Macacus, 

 •which is not found either in the Lemur or in the Marmoset. 



General Desckiption of the Brain. 



The Marmoset has a small brain, and the surface is broken by unusually 

 few fissures. On the external surface the Sylvian fissure (F. S., fig. 2) is the 

 most conspicuous, and there is also an indication of a lateral sulcus (f. pa.) on 

 the temporal lobe. On the under side of the temporal lobe the rhinal fissure 

 (f. rh.) is found, and it may be noticed that it does not come so far around as 

 in the Lemur, where it is seen on the external surface. Thus in the Lemur 

 there is a larger space between the hippocampal and the rhinal fissures, and, 

 therefore, a more extensive olfactory area than in this animal. On 

 the orbital surface a small orbital sulcus appears. An unbranched 

 calcarine fissure (f. cal.) is seen on the mesial surface extending from 

 the hippocampal nearly to the extremity of the pole. A small hippo- 

 campal tubercle lies in front of this hippocampal fissure, and a short inter- 

 calary sulcus appears above the corpus callosum, while in the frontal region 

 there is an indication of a small fissure. These sulci, however, are only 



VOL. LXXXII. — B. L 



