i 5 6 



THE ORIGIN OF VERTEBRATES 



muscles from the cranium to the shoulder-girdle, innervated by the 

 Xllth (hypoglossal) nerve. The ventral series of segments give 

 origin to the musculature supplied by the trigeminal, facial, glosso- 

 pharyngeal, and vagus nerves. 



Also, the afferent or sensory nerves of the skin over the whole of 

 this head-region are supplied by the trigeminal nerve, while the 

 afferent nerves to the visceral surfaces are supplied by the vagus, 

 glossopharyngeal and facial nerves. 



In van "Wijhe's original paper he arranged the segments belonging 

 to the cranial nerves in the following table : — 



As is seen in the table, van Wijhe attempts to arrange the cranial 

 secrmental nerves into dorsal and ventral roots, in accordance with 

 the arrangement in the spinal region. In order to do this he calls 

 the Vth. Vllth, IXth, and Xth nerves dorsal roots, although they 

 are not purely sensory nerves, but contain motor fibres as well. 



It is not accidental that he should have picked out for his dorsal 

 roots the very nerves which form Charles Bell's lateral series of 

 roots, inasmuch as this system of lateral roots, apart from dorsal and 

 ventral roots, really is, as Charles Bell thought, an important separate 

 system, dependent upon a separate segmentation in the embryo of 

 the musculature supplied by these roots. This segmentation may 

 receive the name of visceral or splanchnic in contradistinction to 

 somatic, since all the muscles without exception belong to the visceral 

 group of striated muscles. 



