The Luwer Portiun of the Human Brain-Stem. 35 



the brachium conjunctivum. Lateral to the caudal portion of the median 

 nucleus (figure 3) lies the radix descendens with its accompanying nuclear 

 material, forming the nucleus nervi vestibuli spinalis. From lateral view 

 (figure 2), the general triangular shape of the nucleus can be made out. The 

 apex of this triangle projects laterally and ventrally to meet the incoming 

 vestibular nerve. With this brief general conception of the whole nuclear 

 complex we may proceed to a more careful description. The whole nuclear 

 mass may be said to exhibit three surfaces for examination: dorsal, mesial, 

 and lateral. The ventral surface is lost in the sloj^ing of the ventral surface 

 into the lateral. These surfaces will be described under the various nuclei 

 comprising the complex. 



NUCLEUS NERVI VESTIBULI MEDIALIS. 



This portion of the nucleus extends from the cephalic limit of the gracile 

 nucleus to the caudal border of the nucleus of the sixth nerve (figure 3). 

 Laterally it is bounded by the nucleus nervi vestibuli spinalis in its caudal 

 half and in its cephalic half by the corpus restiforme, except in the region 

 of the nucleus nervi vestibuli lateralis. The nucleus may be divided, for 

 description, into a narrow caudal half and a widened cephahc portion. On 

 dorsal view (figure 3) , the nucleus shows a fairly smooth surface which .slopes 

 ventrally toward the mid-line. Beginning below as a narrow strip of nuclear 

 material with its long axis dorso- ventrally (figure 11), the nucleus widens 

 but slowly in its caudal half. At the region of the opening of the lateral 

 recess into the fourth ventricle, it abruptly projects laterally, almost attaining 

 the mesial limit of the dorsal cochlear nucleus and covering dorsally the 

 radix descendens. As the opening of the lateral recess closes cephalad the 

 nuclear surface under the ventricular floor narrows (figure 12). When 

 viewed dorsally (figure 3) the mesial border of the nucleus exhibits a cephalo- 

 caudal direction with a deflection toward the mid-line as it ascends. In the 

 region of the cephalic pole of the nucleus nervi hypoglossi (widest portion 

 of the nucleus intercalatus) the mesial border of the median vestibular cell- 

 mass shows a marked lateral notch. Above this is a slight transverse 

 elevation across the nucleus as it widens out. At the lower limit of the sixth 

 nucleus the mesial border curves rather sharply laterally and then turns 

 cephalad again for a short distance. But from the point of occurrence of 

 this lateral deflection this main vestibular cell-mass is considered as the 

 superior nucleus. The lateral border of the median vestibular nucleus, after 

 the short caudal portion which ascends almost parallel to the mesial border, 

 runs cephalad and somewhat laterally. It is, in the main, a fairly straight 

 border showing some irregularities, especially one gentle lateral projection 

 just cephalic to the ventricular portion of the corpus ponto-bulbare. This 

 lateral margin continues as a smooth, straight surface to the formatio reticu- 

 laris in a direct dorso-ventral direction the line of separation from the 

 nucleus spinahs of the nerve. At the caudal limit of the lateral recess the 



