256 THE LOWER PRIMATES 



impulses which arise in the proprioceptive organs of the upper extremity 

 and are destined for the cerebelkim. 



THE NUCLEUS OF ROLANDO 



The remaining nuclear structure in the dorsal sensory field, namely, the 

 nucleus of Rolando (substantia gelatinosa trigemini) accounts for the sensory 

 innervation of the face and of the head rostral to the interparietal line. The 

 exact course followed by the hbers conveying discriminative sensibihty from 

 the trunk, from the neck and from the back of the head is not so well under- 

 stood as the tracts which constitute the main conduction pathway from the 

 extremities. It is possible that many of the fibers from the trunk, back of the 

 head and neck make their way to the oblongata after relay in the reticular 

 formation. They may incorporate themscKes in the great sensory pathways 

 of the dorsal columns to receive their relay in the nuclei of Goll, Burdach and 

 Rolando. In any event, these axial fibers, representing the distribution of the 

 dermatomes in the trunk, in the neck and in the back of the head, constitute 

 more or less constant factors which in all probability vary but little from 

 species to species. It is unlikely that any great variation, either in the capac- 

 ity of sensibility or in the demands for conduction, arises in connection with 

 the trunk. Such modifications as do occur appear to be induced by conspicu- 

 ous variables such as the tail, the forelimb and the hindlimb. Thus it might 

 be expected that in an animal possessed of a highly efficient prehensile tail, 

 the nucleus of Goll would appear in larger dimensions than in an animal 

 either possessed of no tail or having one of much more generalized functional 

 significance. The chief nuclear expression connected with the development 

 of the tail appears in the nucleus of Bischoff. The development of the hand 

 affects the column of Burdach which is much larger in animals having a high 

 degree of manual differentiation than in those manifesting but slight differ- 

 entiation of this kind. 



