536 p. E. SMITH 



Figure 45 is through the posterior poles of the cerebral hemi- 

 spheres, caudad to the foramina of IVIonroe. The hippocampal 

 commissure is seen, and separated from it by a layer of cells is the 

 anterior commissure. The ventral sulcus of the diencephalon, 

 which can be traced to the interventricular foramina, is present 

 and separates the hypothalamus from the pars ventraUs thalami. 

 The sulcus medialis is indistinctly seen separating the pars dorsalis 

 thalami from the pars ventralis and, as pointed out by Herrick, is 

 a continuation of the sulcus Umitans of His. By tracing through 

 the series at this region the lateral extension of the cavity, 

 in the dorsal region, can be identified as the sulcus dorsaUs. 

 Between this and a stage just before hatching, the brain has 

 rapidly lengthened, with a partial loss of the cerebral flexure. 



In a 23 mm. larva this process of lengthening has continued so 

 that the brain has assumed nearly its adult shape. Figures 48 

 to 51 are transsections through the fore-brain of a larva of this 

 size. By tracing through the series the septum ependymale is 

 seen to have a much greater dorso-caudal extension than in the 

 previous stage, but as yet there has been but a slight migration of 

 cells into it from the pars ventralis. The primordium hippocampi, 

 however, has become much thicker. The sulci of the diencephalon 

 are more distinct than in the pre\'ious stage. 



In a 30 mm. adult the morphological features are about the same 

 as described for the full-grown adult. The brain has increased in 

 length over the previous stage and the sulci have become much 

 more distinct. 



The most striking feature of the fore-brain of this form is the 

 great size of the lateral walls. The major part of the massive 

 walls enter into the striatum complex or pars ventro-lateralis of 

 the cerebral vesicles. When lar\-ae of this form are compared with 

 species such as Amblystoma punctatum or Salamandra atra, this 

 massiveness is very stl-iking. The relation of the plexuses, the 

 velum transversum, and the paraphysis has been described under 

 the "Development of the epiphysis," It has not been possible 

 to identify the various tracts with the technique employed in this 

 study. 



