MORPHOLOGY OF THE FOREBKATN 445 



plex tracts with the other three parts of the hemisphere. Its 

 connections show clearly that it corresponds, at least in pare, with 

 the nucleus sphaericus of the reptiles and the lobus pyriformis 

 of the lower mammals. 



The pars dorso-medialis (eminentia pallialis medialis, Gaupp ; 

 septum, P. Ramon y Cajal; primordium hippocampi, Kappers). 

 In the frog the whole of this part becomes primordium hippocampi 

 but in some of the urodeles it seems probable that only its medial 

 portion should be so designated. It extends the entire length of 

 the hemisphere. In front of the lamina terminalis it is bounded 

 ventrally by the fissura limitans hippocampi; behind this level 

 it forms the whole median wall of the hemisphere. For its entire 

 length it forms the thickest part of the wall. 



At its rostral end the primordium hippocampi is enlarged and 

 here it receives secondary olfactory fibers from the olfactory bulb, 

 and is connected by a great mass of unmedullated ascending and 

 descending fibers with the underlying nuclei of the septum. All 

 portions of the primordium are connected by strong association 

 tracts with the dorso-lateral part of the hemisphere. The fibers 

 of the commissura pallii anterior arise throughout its mass and 

 P. Ramon y Cajal ('05, fig. 4) figures a Golgi impregnation of this 

 commissure which shows that the free terminal arborizations of 

 its fibers after decussation also reach the lateral wall of the hemi- 

 sphere directly. 



The cells of the primordium hippocampi are arranged diffusely, 

 being scarcely more dense next to the ventricle than elsewhere; 

 but there is no true cortex developed except perhaps atthedorso- 

 median angle of the hemisphere. P. Ramon y Cajal ('05, p. 185 

 and fig. 7) describes here a superficial layer of tangential cells 

 which have well differentiated axons leaving the cell body or the 

 base of one of the thick dendrites and passing ventrally along the 

 medial superficies of the hemisphere. I have impregnations of 

 these cells in Golgi preparations of Rana pipiens which show thac 

 in the rostral half of the hemisphere they extend from the dorsal 

 angle ventrally along the entire medial surface of the primordium 

 hippocampi instead of being limited to the dorsal angle as figured 

 by Ramon y Cajal. Medullated fibers which I consider to belong 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO. 5. 



