424 THE INTERMEDIATE PRIMATES 



The dorsal sensory field is represented by the eokinins of Goll and of 

 Burdach (CG,CB), together \\ith the substantia gelatinosa trigemini 

 (NR) and its aeeompanying deseending trigeminal traet (Trd). A com- 

 parison of these elements shows that the eohunn of Burdach has increased 

 in size relatively to the cokmm of Goll. It is evident froni this relation that 

 the sensory territories of the upper extremity of gibbon have gained in promi- 

 nence. This advance is no doubt consecjuent upon the high degree of brachial 

 and manual specialization essential to the animal's arboreal life. The com- 

 paratively small size of the luicleus of Rolando ( N R ) indicates that much of 

 the tactile direction of locomotion must have been delegated to a more effec- 

 tive and highly specialized hand. 



In the circumferential zone are the ascending libers of the spinocere- 

 bellar tracts ( Fie, Gow). The medullary area surrounding the ventral gray 

 column contains the Deiterso-spinal tracts (DT), while in the intermediate 

 zone are the rubrospinal and spinothalamic tracts ( Rst, Spt). 



LEVEL OF THE CAUDAL EXTREMITV OF THE INFERIOR OLIVE (FIG. 200) 



Here the transverse diameters of the axis have increased considerably. 

 This change especially aflects the dorsal sensory field, due to the appearance 

 in it of the nuclei of Goll and Burdach ( NG, NB). Both nuclei are large but 

 by actual measurement the nucleus of Burdach has a volume about twice 

 that of Goll. The latter nucleus shows no median specialization characteristic 

 of the nucleus of Bischofl. Since the gibbon does not develop a tail, the 

 absence of this unpaired median nucleus might be expected. Connected with 

 Burdach's nucleus there is a large isolated mass which constitutes the nucleus 

 of Blumenau (NBl). The substantia gelatinosa presents marked prom- 

 inence and is in relation with a descending trigeminal tract (Trd) of 

 considerable size. Estimated as a whole, the dorsal sensory fietd denotes 

 the apportionment of the afferent influx. The territory of the upper extrem- 



