648 C. JUDSON HERRICK AND JEANNETTE B. OBENCHAIN 



The subhabeniilar lobe is bounded below by a distinct longi- 

 tudinal sulcus, here termed the sulcus intermedius thalami (fig. 

 3, s.i.), which communicates in front with the sulcus thalamicus 

 1 and behind with the recessus metathalamicus. The sulci which 

 separate the three vertical ridges last described are named re- 

 spectively the first, second and third thalamic sulci (fig. 3). 

 , The sulcus thalamicus 1 communicates below with the sulcus 

 medius and above it forms the posterior boundary of the pri- 

 mordium hippocampi, terminating dorsally in the prehabenular 

 recess, which in turn communicates anteriorly with the saccus* 

 dorsalis. 



The lobus medius thalami occupies the mid-thalamic region 

 (fig. 3, l.m.). It is bounded above by the sulcus intermedius 

 and in front by the eminentia thalami and sulcus thalamicus 2. 

 Behind, its upper part is bounded by the recessus metathalami- 

 cus and its lower part is continuous with the tegmentum above 

 the sulcus limitans of His. Ventrally the sulcus medius forms 

 part of the boundary, but the posterior part of the lobus medius 

 is continuous with the dorsal part of the lobus ventralis. The 

 nucleus primus thalami of Schilling ('07, p. 432) is composed of 

 the cells of this lobe, and probably also those of the eminentia 

 thalami. These cells are smaller and more diffusely arranged 

 than are those of the lobus ventralis (figs. 8, 9). 



The lobus ventralis thalami has already been mentioned as an 

 eminence which crosses the site of the sulcus limitans of His, 

 which is here obliterated (fig. 9). 



The e7ninentia thalami is a narrow vertical ridge lying above the 

 sulcus medius and in front of the lobus medius and lobus sub- 

 habenularis (figs. 3, 4, 7, em.th.). It is produced by a prolifer- 

 ation of nerve cells among which pass the fibers of the tractus 

 olfacto-habenularis of the stria meduUaris system. It forms part 

 of a vertical ridge extending dorsalward from the sulcus mediu s 

 (fig. 4) and terminating above in the eminentia fimbriae. The 

 characteristic laminated arrangement of its cells is limited to 

 the region between the sulcus ventralis and the sulcus interme- 

 dius. Above the latter sulcus is a lower eminence containing few 

 cells and full of fibers of the stria medullaris system (fig. 7) and 



