SPINAL NERVES 



125 



hemispheres. They follow a definite pattern determined by differentiation of 

 areas in the grey matter, which by their own growth, as well as by pressure on 

 adjoining areas, produce the folding of the cortex. The subject will be fully 

 treated of in the descriptive account of the brain (see Neurology). 



PERIPHERAL NERVOUS SYSTEM. 



Spinal nerves. In the human embryo of the third week the rudiments of the 

 inal ganglia are connected together by a continuous dorsal band, which extends 



VII 



VIII a.v. IX X XII XI 



fore-bruin 



ham itphe 



1 T. 



1 S. 



1 L. 



FIG. 1G9. KECONSTRUCTION OF THE SPINAL AND CEREBRAL NERVES OF A HUMAN EMBRYO 

 6'9 MM. LONG. (After His.) 



V, ventricle; A, auricle of heart; L, liver; a.v., auditory vesicle; Fr.g., Froriep's ganglion. 

 The Roman numerals indicate the cerebral nerves. 1 C., first cervical ; 1 T,, fir.it thoracic ; 1 L., first 

 lumbar; 1 S. first sacral nerve. 



from the auditory vesicle along the neural tube to its extreme tip (Streeter). 1 

 Though there are no signs as yet of dorsal roots, the ventral roots are present, 

 and the ventral ends of the ganglia end diffusely among them as they pass out 

 towards the myotomes (Streeter). The ganglion- crest becomes interrupted in the 



1 Amer. Jour, of Anat. iv. 1905. 



