The Loiver Portion of the Human Brain-Stem. 23 



the hypoglossal nerve and extends but a short distance upward, always 

 median to the nucleus intercalatus. 



Lateral to the nuclei of tlie hypoglossal nerve and of the funiculus teres 

 lies the nucleus intercalatus. This is represented on the surface by a rather 

 elongated diamond-shaped elevation lying lateral to the eminentia hypo- 

 glossi and the eminentia of the nucleus funiculi teretis, and mesial and 

 cephalic to the ala cinerea. While the area plumiformis extends caudally 

 to the calamus scriptorius, as pointed out by Retzius and Streeter, the 

 nucleus intercalatus shows its caudal end at the extreme dorsal projection 

 of the area hypoglossi, extending from this point cephalad to the nucleus 

 nervi abducentis. Streeter pictures the nucleus intercalatus as ending in the 

 area of the striie medullares, in which region the area plumiformis ends, but 

 in this adult brain-stem the nucleus extends considerably farther cephalad. 

 The cephalic portion of the nucleus then extends beyond the superior limit 

 of this area plumiformis. 



Situated laterally to the nucleus nervi hypoglossi and to the nucleus 

 intercalatus, and mesially to the nucleus fasciculi gracilis and nucleus nervi 

 vestibularis, lies the ventricular one-third of the nucleus alae cinerei3e (figures 

 3 and 11). This is represented on the ventricular floor by the fovea vagi 

 or ala cinerea, the middle of the three original triangles in the caudal half 

 of the ventricle. This area shows a marked depression in the ventricular 

 floor in its superior portion, corresponding to the place where the nucleus 

 alse cinerese dips ventrally to the vestibular nucleus and nucleus intercalatus. 

 Caudally, the area shows a dorsal eminence, lying directly over the marked 

 dorsal angle of the nucleus al cinerese. No attempt has been made to 

 model or correlate in any way the loose vascular tissue in the area postrema 

 of Retzius. The cephalic limit of the nucleus alie cinerese, when related 

 to the anatomy of the floor of the fourth ventricle, lies ventral to the nucleus 

 nervi vestibularis medialis at a level with the middle of the nucleus funiculi 

 teretis. This corresi)onds to Streeter's cephalic limit. 



Streeter gives the area acustica as that part of the ventricular floor 

 which lies lateral to the anterior fovea and the fovea vagi and the lateral 

 furrow connecting the two. This large area is divided into the median 

 vestibular field and a lateral cochlear region. As seen from inspection of 

 figure 3, these two regions are, in this adult brain-stem, occupied by th(^ two 

 nuclei that of the vestibular nerve and that of the cochlear nerve. Streeter 

 places the vestibular nucleus in his diagram of the ventricular floor as lying 

 entirely lateral to the lateral furrow. The median nucleus of the vestibular 

 nerve in the reconstruction extends mesially to the lateral furrow in the region 

 just caudal to the sixth nucleus, in which situation it seems on cross-section 

 to occupy most of the region just beneath the ventricle. In general, the 

 vestibular nucleus follows the gentle convexity of the lateral furrow, but in 

 the region just caudal to the nucleus nervi abducentis it shows a rather 

 marked angular convexity and concavity. Streeter does not give the cephalic 



