8o6 MAN 



mediate area, the rubrospinal (Rst), spinothalamic (Spt) and Dciterso- 

 spinal (DT) tracts. 



LEVEL OF THE CAUDAL EXTREMITY OF THE INFERIOR OLINARY 



NUCLEUS (FIG. 344) 



Here the general configuration of the section has changed considerably 

 due to expansion incident to the dorsal migration of the central gray matter. 

 In the ventral position, occupying the usual place on either side of the ventro- 

 medial sulcus, are the dense bundles <:f the pyramids ( Py). It is possible 

 at this le\el to obtain some estimation of the relative unportance ol the 

 pyramidal system in the human neiu-axis. At this Ie\'el the pyramidal libers 

 occupy at least a ciuarter of the entire cross section. This clearix nulicates 

 to what extent the function of volitional control over somatic musculature 

 has expanded to meet new demands Imposed b\ the human race. The.pyrami- 

 dal system has jirogressively increased from the lowest extremity of the 

 primate series to this point. 



Dorsolateral to the pyramid is a mass of gray matter heretofore not 

 apparent in the section, the caudal e\trcmit\ ot the interior olivary 

 nucleus (10). The central gray matter (Cen) has become more circular 

 in outline, containing the central canal near its center. It is almost entirely 

 surrounded by arching nu'dullated libers rising for the most part Irom 

 the nucleus of Coll and sweeping to the ia])lu- to form the lower portion 

 of the decussation of tlu' mesial lillet (Mfx). These arching axons are the 

 interna! arcuatt' libers and represt'iit the decussation in thepathwa\' lor the 

 conduction of impulses from the leg and foot. The dorsal sensory field shows 

 in this section as in lower IcacIs the disproportion between the column oi 

 Goll and column of Burdach. These two dorsal columns arc still clearly 

 demarcated by the dorsal paramedian sulcus. In the most lateral position 

 of the dorsal sensorv held is the substantia gelatinosa trigemini or nucleus 



