THE NERVOUS SYSTEM. 



501 



Roof plate 



Floor plate 



FIG. 439. Transverse section through the trigeminal region of the rhombic brain of a 10.2 mrru 

 human embryo, a. W., Spinal V; V. s., Gasserian ganglion; V. m., part of efferent root of 

 V nerve. His. 



FIG. 440. Part of a transverse section through -the rhombic brain of a chick embryo toward the 



fourth day, showing the trigeminal roots. Cajal. 

 A, part of the efferent (masticator) nucleus of the V; B, efferent root of the V; C, bipolar cells of 



the Gasserian ganglion; D, beginning of descending tract (spinal V) formed by the central 



processes of C. 



