6io THE HIGHER ANTHROPOIDS 



The Dorsal Medullary Nuclei 



One of thf dorsal sensory nuelei has already made its appearance. The 

 nueleus of CjoII is present and oeeupies ahnost tlie entire \entrodorsaI extent 

 of the eohiniii of Coll. It is narrow, compressed from side to side and con- 

 nected at its base \\ ith the central gray matter. On all sides, except at its 

 point of junction with the central gray matter, it is enveloped h\ hbers of the 

 column of Goll. The sensory nucleus of Burdach first appears at a level 

 somewhat higher than the caudal e\trcniit\ of the nucleus of Goll. It is dis- 

 tinguishable as a thickening in the dorsal surlace of the central gray matter 

 or the junction of the dorsal horn with the central gray matter. This sessile 

 condensation of nuclear material gradually becomes more promment. 



A lateral divergence is characteristic of all of the dorsal gray structures, 

 being produced by the opening of the fourth \entricle which tends to force 

 all of the dorsal structures further from the median line. The dorsal extremity 

 of the tuicleus of Goll becomes expanded laterally and overhangs tln' more 

 ventral structure at a level below the opening of the expanding lourth 

 ventricle. Tlu' nuclear material becomes much more extensive near the 

 dorsal peripher\ of the axis and presents a marked tendency to accumulate 

 laterally. This arrangement is characteristic also of the nucleus ol Burdach, 

 the dorsal extremity of w hich becomes hea\ier and shows the same tendency 

 towards lattwal extension. In some places it is carried so far as to oNX'rhang 

 the substantia gt'latinosa trigemiiii. 



In the caudal region of the xeiitricular opening the lateral walls of tlu' 

 fourth ventricle on each side are lorined by the nucleus of Goll. Higher up the 

 nucleus of Goll is gradually separattcl from the lateral borders of the lourth 

 ventricle by the interposition of the wstibular com]3lex between it and 

 the ventricular wall. 



