THE NERVOUS SYSTEM. 



471 



Roof plate 



FIG. 401. Transverse section through the trigeminal region of the rhombic brain of a 10.2 mm. 

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

 V nerve. His. 



FIG. 402. Part of a transverse section through the rhombic brain of a chick embryo toward the 



fourth day, showing the trigeminal roots. Cajal. 

 Aj 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 



Drocesses of C. 



