BRANCHIAL SENSE ORGANS OF ICHTHYOPS1DA. 209 



It is interesting to notice that if my views be correct the nose and 

 ear are the only remains of the branchial sense organs 1 in the adults 

 of higher Vertebrates. They have survived with a possible change of 

 function, while the other branchial sense organs have disappeared 

 except in the first stages of the embryo, and are then only transitory 

 structures. 



The Morphology op the Supra-branchial Nerves. 



This point has, I think, been sufficiently demonstrated in the general 

 part of this work. The supra-branchial nerves are merely concerned 

 in extensions of the branchial sense organs to a distance from the 

 ganglia. They are erroneously called dorsal, for this condition when 

 acquired is purely secondary. 



Any commissural nature of some of these branches, as suggested by 

 Marshall and Spencer, is out of question. None of them are remains 

 of the neural ridge. Still less can I accept Spencer's recent suggestion, 2 

 that " the two curious branches which unite respectively the fifth and 



seventh and fifth and third cranial nerves may be regarded 



as persistent parts of the lateral nerve which united the ganglia of the 

 sense organs along the lateral line in the head, and which, separating 

 from the skin, have come in the course of development to occupy a 

 much deeper position, together with the ganglia, with which they 

 preserve their primitive connection." 



These " curious branches " are portions of fused supra-branchial 

 nerves, as a glance at the diagrams (figs. 46 and 51) will show. 



The Relations op the Head and Trunk in Vertebrates. 

 Many attempts have been made to homologise the components of 

 the segments of the head and trunk, aud naturally such attempts have 

 extended to the nerves. The spinal nerves, it is hardly necessary to 

 say, present anterior and posterior roots, the latter of which are 

 ganglionated. Such a state of affairs has been sought for also in the 

 head, but in face of the facts previously recorded it is at least doubtful, 

 even if the existence of cranial anterior and posterior roots be granted, 

 whether these can be homologised with those of the spinal nerves. 

 The posterior roots of cranial and spinal nerves develop differently, for 



1 Professor F. E. Schultze notwithstanding, the possibility that the taste buds of the 

 tongue of higher Vertebrates are also to be referred to those sense organs must be borne in 

 mind. Their innervation by the glossopharyngeal is, in this connection, very suggestive. 



8 Spencer, * Notes on the Early Development of Rana temporaria,' p. 12. 



