Kingsbury, Brain of Nectuius. 151 



study of the brains of embryo Dianyctyliis and the Lamprey 

 states that "upon embryological grounds it seems as though the 

 rhinencephal were equally entitled with the prosencephal to a 

 share of the aula as a mesal cavity." 



It is difficult to determine how much of the combined ol- 

 factory lobes and cerebrum in Ncchtrus, may be considered as 

 belonging to the former. A slight vertical furrow upon the 

 endymal surface of the mesal walls, slightly cephalad of the 

 caudal limit of the olfactory glomerules, may possibly be re- 

 garded as indicating its limit, in the mesal walls. The hori- 

 zontal sections, Figs, 34 and 35 show the general relations. 

 The olfactory nerves spring from the lateral and ventro-lateral 

 portion of the lobes. Completely encircling the olfactory glom- 

 eruli, in which the nerve fibers end, is an area of ectocinerea, 

 first appearing on the lateral aspect and spreading cephalad, 

 both dorso-mesad and ventro-mesad, to complete the circle in 

 the cephalic portion of the mesal surface of the apposed lobes. 

 A slight furrow outlines this area so enclosed, more marked on 

 the lateral surface, fainter on the dorsal and ventral aspects. 

 Fig. 33 shows a transection through this region of the brain. 



Prosencephal. — The prosencephal is of the characteristic 

 amphibian form and structure. The extent and relations of 

 alba and cinerea are shown in the series of transections. Figs. 

 28-33, 42- The ventro-lateral walls, in which the peduncular 

 tracts are lost, representing undoubtedly the basal ganglia of 

 Edinger, the striatums, form but faint swellings into the para- 

 coeles, these being most marked in the region of the portas. The 

 mesal walls are spoken of subsequently in connection with th? 

 cerebral commissures. The entocinerea extends to the ectal 

 surface of the prosencephal only in three places, — (i) at the 

 caudal ends of the cerebrums where the walls are quite thin, (2) 

 at the meson in the terma cephalad of the cerebral commissures, 

 and (3) in the mesal wall cephalad of the terma ; here it is quite 

 extensive. Immediately cephalad of the terma the mesal walls 

 of the cerebrum are formed only of pia and endyma which in 

 the region consists of two to three layers of cells (Fig. 31). 

 This is soon succeeded farther cephalad by true nervous parietes 



