The Lower Pcniion of the Human Brain-Stem. 57 



cephalo-caudal sulcus there arises a single caudally directed fissure, short 

 and superficial, separating off a gyrus of the lobe which lies upon the mesial 

 wall of the deep furrow. The portion of this lobe which lies between the 

 cephalo-caudal and third transverse sulci runs caudally and somewhat 

 laterally. This consists of one main convolution, broken into two parallel 

 gyri by a middle superficial sulcus which follows the general direction of the 

 convolution but has a gradual curve, the convexity being mesial. Laterally, 

 the lobe projects around to form the third or caudal lateral lobe (figure 2). 



Caudal to the obliquely coursing third transverse sulcus (c) lies the 

 caudal lobe of the dorsal surface (figure 7). It is very small and does not 

 extend to the lateral surface. It consists of two main gyri, divided in their 

 mesial portion by a short transverse secondary sulcus, which arises at the 

 caudal end of the hilum. The more cephalic of the two gyri lies more 

 dorsal than the caudal gyrus in its mesial part, but laterally the two gyri 

 approach and fuse with one another to form a flat and wide lateral convolu- 

 tion. The caudal part of the gyrus is continued down as a small s]nir to 

 form the inferior pole of the olive. 



Bounded superiorly by the lateral part of the first dorsal transverse 

 fissure (a), and mesially by the cephalo-caudal furrow, the lateral dorsal 

 lobe occurs (figure 7). Its main axis is ajiproximately cephalo-caudal. At 

 the upper mesial part of the lobe there is l)ut one convolution, but as this 

 goes laterally and caudall}', it is severed into the two main gyri of the lobe 

 by a fairly deep oblicjue sulcus which parallels the main cephalo-caudal 

 sulcus for some distance and then curves laterally and caudally to separate 

 the first and second convolutions of the middle lateral lobe. The gyrus 

 lying above this sulcus widens somewhat as it curves upon the lateral surface 

 and shows a shallow but broad groove upon it, becoming the superior con- 

 volution of the lateral middle lobe (figure 2). The gyrus lying mesial to 

 and inferior to the sulcus just described, continues inferiorly and slightly 

 laterally as a rather narrow convolution, then rapidly widens out and curves 

 over into the two lower gyri of the lateral middle lobe. The most inferior 

 part of this descending convolution is separated from the main mass by a 

 shallow curving sulcus, which ends as the lateral and dorsal surfaces meet. 

 Above this sulcus the beginning of a rather deep lateral fissure is seen, the 

 furrow which divides the convolution into the two lower gyri of the middle 

 lateral lobe. The most inferior portion of the gyrus is composed of the 

 caudal spur or lowest gyrus of the lateral middle lobe. 



The lateral view of the olive (figure 2) suggests, more than any other, 

 the idea of a rotation of the superior pole of the olive. The slope of the main 

 axis of the olive, when viewed from the side, is dorsal in the cephalic region, 

 the mesial part of the cephalic lobe of the dorsal surface projecting far more 

 dorsally than the other two-thirds of the nucleus. The lateral portion of 

 this lobe is somewhat dorsal to the rest of the nuclear mass on lateral \iew, 

 a fact in accord with the obtuse angle maile l)y the transverse axis of the 



