The Loioer Portion of the Human Brain-Stem. 59 



or small gyrus, poorly separated by a shallow, ill-defined groove. The 

 inferior convolution shows a marked crescentic outline, the concavity of 

 the crescent being directed cephalad. Interiorly, this middle lateral lobe is 

 bounded l)y the lateral termination of the dorsal cephalo-caudal sulcus; the 

 sulcus ends in the mid-line of the lateral surface, but its direction is continued 

 by a short curving groove, which leads cejjhalad and ventrally. 



Inferiorly, there occurs the caudal lobe of the lateral surface (figure 2). 

 This is bounded in its cephalic part by the sulcus just mentioned as forming 

 the inferior limit of the middle lobe. Caudally the lobe is bounded by the 

 lateral superficial ending of the third transverse gyrus and by the polo of 

 the nucleus, which the lobe forms on this surface. The lobe itself is com- 

 posed of a narrow gyrus on its dorsal side, a continuation of the dorsal third 

 lobe. Just caudal to the spur on the third convolution of the middle lobe, 

 the caudal lobe widens into a broad convolution, which curves ventrally and 

 cephalad into the ventral surface (figures 1 and 5). A single, shallow cephalo- 

 caudal fissure occurs on the ventral one-third of this lateral caudal lobe. The 

 whole caudal lobe comi)rises one-sixth to one-seventh of the lateral surface. 



On direct ventral view (figure 5), the ventral leaf of the inferior olive 

 comprises but the lateral half of the field, while the ventral surface of the 

 dorsal leaf shows in the mesial portion. As described by Mi.ss Sabin in the 

 new-born, the course of the ventral fissures is radial, the central jwint being 

 slightly inferior to the middle of the ventral border of the hilum. Superior 

 to this point of radiation lies the ventral part of the cephalic dorsal lobe; 

 inferior to it the ventral prolongation of the middle lateral lobe and the 

 dorsal lateral lobe, while far caudalwards, forming the inferior limit of the 

 hilum, occurs the ventral part of the dorsal caudal lobe. The ventral aspect 

 is concerned with a marked ventral bulging of the middle part of its surface, 

 in the inferior i)ortion of the cephalic lobe and in the ventral part of the 

 middle lateral lobe. From this jirominence the ventral surface slopes 

 dorsally, both cephalad and caudad, but this slope is soon reduced to fairly 

 flat planes, which curve over into the cephalic and caudal surfaces. The 

 lateral outline, on ventral inspection, exhibits a marked lateral i)rominence 

 of the inferior portion of the cephalic lobe, overhanging, if such a term be 

 possible, the lateral middle lobe (figures 1 and 5). Caudal to this, the lateral 

 middle lobe develops a lateral ])rominence in its lower portions, overhanging 

 in turn the lateral caudal lobe, which differentiates itself sharply at a 90 

 angle from its cephalic neighbor; on the inferior extremity occurs the caudal 

 tip of the caudal dorsal lobe (figures 1, 5, and G). 



From the center of radiation, which really forms the caudal ventral 

 portion of the cephalic lobe, the most striking fissure is that which arises 

 from the cephalic border of the center and passes cephalad in a fairly direct 

 cephalo-caudal direction, to end superficially on the cephalic surface of the 

 cephalic lobe (figures 1 and o). Between this furrow and the ventral border 



