ORIGIN AND STRUCTURE OF THE HEAD 95 



roots belonging to the head region and not, as first suggested 

 by Balfour (1878, p. 205) and afterwards worked out 

 especially by FRORlEP and FuRBRlNGER, as elements 

 of post-cephalic origin that have only secondarily shifted 

 forwards into the occipital region, losing their dorsal roots. 

 Moreover, ventral roots have since been discovered in 

 Amphioxus also (SCHNEIDER, 1879, p. 15), and here evidently 

 occur also in the anterior segments which in Craniates 

 belong to the head. This renders it probable that in the 

 head of the latter ventral roots have been present once 

 and have only secondarily been lost when the myotomes 

 degenerated. Nevertheless, though BalfouR's arguments 

 appear not to hold water, his opinion quoted above is in 

 perfect accordance with the conclusions resulting from my 

 theory, as follows from what has been said on the ventral 

 roots in the first chapter. BALFOUR, evidently imagined 

 the ventral roots to have originated by a process of splitting 

 off from the dorsal roots, which, however, seems to me 

 to be improbable. 



Van Wyhe (1882) has emphasized that the muscles inner- 

 vated by the doisal motor branches of the cranial nerves, 

 the constrictor es of the gills, though striated and voluntary, 

 must yet be considered as visceral muscles, originating from 

 the lateral plate and situated in the wall of the gut. The 

 nerves supplying them accordingly are to be compared to the 

 nerves of the sympathetic system in the trunk. The latter 

 come from the sympathetic ganglia which ontogenetically 

 are derived from the spinal ganglia. Thus the contrast of the 

 cranial ganglia with the latter would be less abrupt than might 

 appear at first sight. Only the splitting off of a sympathetic 

 ganglion has not occurred. This, however, can also be 

 considered as a primitive feature. In Amphioxus the 

 separation of a visceral portion from the spinal nerves 

 equally fails to find place, the dorsal roots being of mixed 

 character. The mixed character of the dorsal roots of the 

 head then is no doubt to be considered as a primitive 

 feature. 



2. There are segmental communications with the lateral 

 organs and, as in Amphioxus, the dorsal roots take their 

 path outside the myotomes. Besides the sympathetic elements 

 the head ganglia thus also contain the lateral line 

 elements which the trunk ganglia have lost, if the concep- 

 tion of the ramus lateralis vagi as a collector is right. 



