THE BR-\IN OF MODERN .\L\N 799 



tion lateral to the nucleus fasciculi teretis and the nucleus hNpoglossi is an 

 elongated and wedge-sh. vation caused by the presence of the nucleus 



intercalaris. Many fine grooves cross this nucleus esf)eciaJIy along its mesial 

 and later rs, the area plumiformis. Lateral to the nucleus intercalaris 



and to the sulcus limitans is the inferior fovea vagi, also known as the ala 

 cinerea. This area presents the middle third of the dorsal vago-glosso- 

 phar^-ngc js which in large part lies on the floor of the fourth ventricle. 



The mesial boundary- of the fovea vagi is formed by the sulcus limitans while 

 its lateral edge is slightly elevated in a cord-like ridge, the funiculus separans 

 of Retzius. Dorsolateral to this funiculus is the area postrema. The pwrtion 

 of the floor of the ventricle lateral to the sulcus limitans forms the area 

 acustica. This consists of a mesial or vestibular field and a lateral or cochlear 

 field. The vestibular field forms a pronounced irregular elevation whose 

 -itords some idea as to the degree of organization in th .ing 



mechanism of man. That this apf>ears to be less than in the arboreal pri- 

 mates is quite evident even u{x>n suj>erficiaJ insp>ecrion. 



The floor of the ventricle is traversed by the striae acusticae. Imme- 

 diately cephalad to the striae acusticae and adjacent to the median sulcus 

 is a rounded elevation formed by the genu of the facial nerve encircling the 

 nucleus abducentis. This is the eminentia facialis. 



The cephalic extremrtv- of the fourth ventricle becomes continuous with 

 the Sylvian aqueduct, dorsal to which are situated the quadrigeminal plates, 

 specialized to form the superior and inferior colliculL Both of these eminences 

 in man apf>ear relati\"ely insignificant, and their surface relief is much less 

 than in the lower and intermediate primates. They seem e\-en less prominent 

 than in the great anthropoids. The sulci sep>arating the two sets of coOiciJi 

 are broader and more shallow than in the other primates. The longitudinal 

 intercollicular sulcus is considerably expanded to form the pineal fossa in 

 which is lodged the epiphysis cerebri. Upwn the lateral surface of the mid- 



