l62 



THE LOWER PRIMATES 



pyramids nor the inferior olivary bodies have any distinct surface relief, 

 nor is it possible to detect any superficial indication of the pyramidal decus- 

 sation. The relative insignificance of the pyramidal system indicates an 



fig. 77. ventral surface of brain stem, callithrix jacchus 

 (marmoset). 



[Actual Length, 22 mm.] 



Key to Diagram, cer. ped.. Cerebral Peduncle; o.N., Optic Nerve; op. ch., Optic Chiasm, trap; 



BODY, Trapezoid Body; ventro med. sulcus, Ventromedian Sulcus. 



extremely limited range of volitional performances and in this respect places 

 the animal even lower in the scale than the lemur. The bulbopontile sulcus 

 is difficult to make out except in fresh specimens, and the pons itself is a 

 flat, narrow band conveying the impression that the animal has not devel- 

 oped a pallio-cerebellar connection capable of producing any large degree of 

 coordinative control over skilled movements. On the dorsal aspect of the 

 oblongata there is a slight mesial eminence indicating the presence of the 

 column and nucleus of Goll. No similar lateral prominence adjacent to it 

 gives surface indication of the column of Burdach. This fact seems to indicate 

 that the tail and lower extremity are more prominent functional elements 

 than the forelimb (Fig. 78). 



