310 THE INTERMEDIATE PRIMATES 



LEVEL OF CAUDAL EXTREMITY OF INFERIOR OLIVARY NUCLEUS (pIG. 1 46) 



At this level the appearance of the cross section has undergone con- 

 siderable change. The principal modification arises from the fact that a new 

 mass of gray matter, hitherto not present, has made its appearance. This 

 is the inferior ohvary nucleus (10) which lies dorsolateral to the fiber 

 bundles constituting the pyramid ( Py ). Dorsal to the chief olive is a smaller 

 mass of gray matter, the dorsal accessory olive, while dorsal to the 

 pyramid and ventromesial to the inferior olivary nucleus are some trans- 

 \'ersely disposed fibers extending mesially toward the raphe. These are 

 fibers of the mesial fillet (Mf) which have undergone decussation. The 

 decussating libers forming the mesial fillet constitute the internal arc- 

 uate fibers, most of which take origin in the nucleus of Goll and form that 

 portion of the fillet which here represents the lower extremity and tail. 

 The pyramid (Py) now has the appearance of a dense bundle occupying 

 the most ventromesial portion of the section. Its diameters, both trans- 

 verse and antero-posterior, give it the proportion of about i to 8 of the entire 

 section. This ratio furnishes some idea as to the relative importance of 

 the pyramidal system in the regulation of motion, particularly if taken 

 in reference to the corresponding system of fibers in the lemur where 

 the proportion appeared to be about i to lo. This increment in the pyra- 

 midal system signifies a functional increase in the regulation of voluntary 

 motion. 



The dorsal nuclei of GoII and Burdach ( N G, N B ) are much increased in 

 size as compared with the lower sections. The nucleus of Burdach ( NB) 

 appears to be considerably larger than the nucleus of Goll fNG), especially 

 if estimated in connccticMi with a number of scattered accessory nuclei 

 surrounding it and usually known as the lateral nucleus of Blumenau. 

 This increase in the nucleus of Burdach still further bears out the impres- 



