196 DEVELOPMENT OF THE SPINAL NERVES, &C. 



spicuous features in successful longitudinal sections of embryos so hardened. In 

 sections hardened with chromic acid only they cannot be seen with the same facility. 



sp. c. spinal cord. gr. grey matter, w. white matter, ar, anterior root. pr. 

 posterior root. x. commissure uniting the posterior roots. 



Figs. Mi, M II. Two sections through the head of the same embryo as fig. B. 

 M I, the foremost of the two, passes through the anterior part of the thickening of 

 epiblast, which becomes involuted as the auditory vesicle. It contains the rudiment 

 of the seventh nerve, VII. Camera. (Zeiss CC ocul. 2.) 



VII. rudiment of seventh nerve. au. thickening of external epiblast, which 

 becomes involuted as the auditory vesicle, n. c. neural canal, ch. notochord. pp. 

 body-cavity in the head. so. somatopleure. sp. splanchnopleure. al. throat ex- 

 hibiting an outgrowth to form the first visceral cleft. 



