134 



NERVOUS SYSTEM 



into which, or through which, the visceral branches of the spinal nerves grow. 

 The nerve-fibres are said to become connected with the cells, and certain of these 

 persist to form the ganglia, while those of the intervening portion undergo changes 

 resulting in the formation of the commissural cords. This view has found little 



hemisphere 



pituitary 

 int. car. art. - 



geniculate g. 

 v. cereb. lot. - 



auditory ves. 



VII nerve 



stapes and 

 stapedial art. 



IX nerve 



v. cerebralis 1. 

 X nerve 



vertebral art 



spinal ganglion 



- spinal ganglion 



FIG. 176. SECTION OF THE HEAD OF A HUMAN EMBBYO OF 15'5 MM. Photograph. (T. H. Bryce.) 



The section will be readily understood if the structures be traced along the line between the two 

 arrows in fig. 175, p. 131. Ill, cavity of diencephalon. 



favour ; and even though the cells may seem to arise in situ, our present knowledge 

 of the composition of the mesenchyme does not warrant our pronouncing all 

 elements in it necessarily mesodermic. The second view is presented in several 

 forms. One account, based more especially on Selachian material, describes the 



