RECONSTRUCTION OF TROGLODYTES NIGER 621 



I'liuT^mij; IiIhts oI the (Kuliim((t<ir iui\ t'. Latcrallx it pri'Sfiits the nuclear 

 spc'ciali/at ion w hieli has hccn h)uiKl rc'<j;uhirl\ to {nkv plncv 111 this jxirt ol the 

 substantia ni^ra in the lower |Miinati' lornis. Laterall\ it eonies into close 

 relation with tlu' mesial ii;eni(.ailate hocl\, but dot's not make actual contact 

 with this nuclear mass. Dorsall\ it is separated Irom the reticular formation 

 by the circumlereiitial libers ol this lormation. 



The Nucleus Ruber 



The nucleus riibcr is a large nuck'ar mass wliich is lirst encountered at a 

 point near the mid-nicsence[)halic le\ c'l. Here it appears as a rounded encap- 

 sulated stiLicture amidst the dccussatinii; libers ol tlu' superior ci'rebcllar 

 l^edunck'. It rapidix mcri'ases in size, occup\ ing almost the t-ntire mesial 

 hall of the mesencephalic rc'ticular formation and extending ujjward into 

 the diencephalon. 



The Central Gray Matter 



The central gra\ matter in the high cer\ ical le\ tis appears identical in 

 form with the ci'iitral gra\- matter of the human adult. It is disposed as a 

 quadrilateral mass surrounding tlu' central canal ol tlu' spinal cord. 



As the oblongatal nuclei (k\t'lop and the mlerior e\tremit\ ol tlu' lloor 

 of tlu' fourth \'entricle is approached tlu' central gra\ matter passes in a dorsal 

 direction, sending backward a thin lamina toward the dorsal |K'ri|)her\- of 

 the neuraxis. As this dorsal migrat ion takes place the qua<lrilateral lorm ol the 

 central gia\ matter undergoes a change. It becomes llattened out and then, as 

 the fourth \entricle opens, the cut ire extent beconu's disposed in a single layer 

 extending from side to side. .A thin la\t-r ofgra.\- matter ri'iiiains in the lateral 

 wall and the roof of the fourth \(.-ntrick' as the sulx'pendx nial gra\ matter. 



In the lower part of the fourth \entrick' the [prominence ol the hxpo- 

 glossal nucleus is easil\ identilud close to the midline. Somewhat abo\e and 



