The Lower Porfioti of the Human Brain-Stem. 55 



arises from the border of the hilum and may be divided into three equal 

 parts for description (figure 7, c). Tlie first portion is deej) and broadens 

 out somewhat as it courses laterally. This portion runs directly transversely, 

 to meet with a fairly deep cephalo-caudal secondary sulcus descending 

 from the third lobe. The main fissure then turns somewhat caudally as a 

 deep and very narrow sulcus (the second portion), which ends as a short but 

 deep cephalo-caudal secondary sulcus fuses with it, and the two continue 

 into the third portion, running cephalo-caudally with considerable lateral 

 deflection. It continues around to the lateral surface to form the inferior 

 limit of the third or caudal lateral lobe. 



These, then, form the foiu- iirincii)al sulci of the dorsal surface of the 

 olive. Unlike the sulci described by Miss Sabin, all of these are continued 

 upon the lateral surface, either directly, as in the case of the cephalic and 

 caudal sulci, or indirectly through the agency of the deep cephalo-caudal 

 fissure as in the case of the middle transverse fissure. Whether or not this 

 deep cephalo-caudal fissure should be considered a principal sulcus is ques- 

 tionable. As seen in the view of this surface (figure 7) the middle transverse 

 sulcus {b) continues into it without interruption and it may be considered 

 as merely the lateral continuation of this principal fissure. But the cei^halic 

 part of the sulcus, extending caudally from above the first main transverse 

 fissure, argues strongly for its consideration as a principal furrow. 



Five distinct lobes may be made out on the dorsal surface as shown in 

 figure 7. These may be considered as the four lobes described b}' Miss 

 Sabin, with the fifth lobe formed by the dorsal surface of the middle lateral 

 lobe. This fifth lobe lies lateral to the main cephalo-caudal fissure, bounded 

 above by the first transver.se fissure and medially and caudally by the fissure 

 to which it lies lateral. The other lobes lie in the regions marked off by 

 the transverse sulci. 



The cephalic dorsal lobe is liy far the largest of the four, occupying 

 about one-third of the whole olivary nucleus and lying cephalic to the first 

 main fissure (figure 7, a). It is subdivided into a superior and inferior 

 portion by a rather shallow sulcus of the secondary order, which travels 

 parallel to the first main furrow. This transverse sulcus takes origin from 

 near the border of the hilum at a point midway between the origin of the first 

 main sulcus and the cephalic end of the hilum. It soon becomes somewhat 

 deeper and sends cephalad a short, broad furrow which contributes to the 

 formation of the gyri in the .superior half of the IoIm'. Continuing hiteral- 

 wards and becoming (juite sujjerficial, it sends caudally, in the middle part 

 of its course, a rather deep but short sulcus, which soon divides into two 

 portion.s a caudal projection, becoming superficial over the gyrus above 

 the first main fissures, and a mesial (more marked) furrow which extends 

 mesially toward the hilum and parallels the first main furrow. AV)(Mit these 

 sulci lie the gyri of the medial portion of the inferioi' half of the cephalic 

 lobe. The secondary transverse fissure, after giving off this caudal sulcus, 



