Herrick, Morphology of Nervous System. 35 



rounding these nearly spherical masses is a cortical band of 

 Hbrous matter containing densely-packed fusiform cells. 

 This cortical portion of each side is produced mesad to 

 unite with its fellow, thus giving rise to the large medi- 

 commissura (m. c. Fig. 6). These bodies are probably what 

 Stieda refers to when he says: "'Ferner schliessen sich die 

 Nervenzellen in den beiden Thalami optici zu einen kugel- 

 nmden Complex zusammen — den Nervenkern der Thalami." 



Note.— Attention may be called to the fact, noticed by Stieda, that 

 there is a small ganglion on the root of the eighth (Plate III, Fig. 2), 

 through which the fibres pass mesad to the very large and protuberant 

 eminentia acustica (Plate III, Fig. 4, E, ac). which projects cephalad, 

 dorsad and mesad into the ventricle below the cephalad part of the cere- 

 bellum. This projection it is. no doubt, which Carus(') refers to as 

 " Ganglion des Hornerven im vierten Ventrikel " which Stieda is una- 

 ble to identify. ■ 



PLATE I. 



Pisj^s. 1-4. Longitudinal horizontal sections of the head of embryo 

 of the guinea-pig at different levels. 



■Pis'. 1- Illustrates the relations of the lateral and third ventricles, . 

 the formation of the plexus (P), and of the hippocampus (H ), as portions 

 of the same fold of cortical substance, and also the existence of two re- 

 gions {a and b). where. the proliferating cells of the ventricular epithel- 

 ium come into relation with the cortex, suggesting the possibility of 

 localized deep origin of the mother cells of the cortex in later stages. 



Fiff. ,.-'. Section of the same brain at a more ventral level, the 

 investing structures being removed. The relations of the striatum to 

 the peduncles is well seen. 



Fi'ir. .y. Similar section from a still lower level, showing results 

 of the strong pons flexture. The medulla and cerebellum are cut 

 transversely, while the paired rudiments of the hypophysis are seen 

 between the Gasser's ganglia. The recess us hi tenth's inferior of the 

 fourth ventricle is nearlj' closed, and the formation of the lateral niduli 

 of the medulla from the cells of its ventricles is just beginning. The 

 dorsad projection of proliferating cells begins to circumscribe the cere- 

 bellum. 



Fig. 4. A section slighth' ventrad to the above, showing especially 

 the dorsad prolongation of the recessus lateralis by which the germin- 

 ative area of the dorsal surface of the cerebellum is produced. It ulti- 

 mately becomes soldered upon the cerebellum, forming a double cellular 

 zone. 



I C. G. C.^RUS, Darstellung des Ncrvensybtems und Hirns, Leipzig, 1S14, p. 17.— 181. 

 L. SriFnA, Ueber den B.tu des centralen Nervensystems der Srhildkrote. 1875. p. 70. 



