CRANIAL NERVES AND SENSE ORGANS OF FISHES. 233 



This table ignores the visceral ("collector") division of the 

 vagus, about which there is still considerable uncertainty. 

 It has been supposed to correspond, posteriorly, to the 

 so-called "visceral" branches of the anterior branchial 

 nerves ; but this can hardly be the case, since each unit 

 in the vagus possesses a "visceral" branch of normal 

 position and distribution. The morphological value of the 

 visceral division of the piscine vagus, therefore, still awaits 

 elucidation.* Another omission in the table is, of course, 

 the spinal accessory and hypoglossal nerves. The latter 

 is undoubtedly represented in the lower vertebrates, 

 where we see that it is formed by the most anterior 

 spinal nerves which have lost their dorsal roots, and 

 which may or may not pass through the cranium, f The 

 condition of these nerves emphasises the fact, admirably 

 illustrated amongst the " Ganoid" fishes, that the verte- 

 bral column has actually played some part in the building 

 up of the skull. The vertebral theory, therefore, though 

 largely false, certainly contained an element of the 

 truth. Hence the hypoglossal nerve, and the spinal 

 accessory also (at any rate, for the most part), belong to 

 a different category from the reminder of the cranial 

 nerves, and should not therefore be ranked with them — 

 if we are to understand by a cranial nerve a nerve 

 related essentially and primitively to the head. 



* A possible explanation of the vagus, I think, is that the branchial 

 nerves are secondarily sympathetic, i.e., in function only, whilst the visceral 

 nerve is primarily sympathetic, i.e., represents a modified portion of the 

 sympathetic, and thus both physiologically and morphologically belongs to 

 that system. Its connection with the vagus is thus a "blind," and of 

 precisely the same significance as the connection of the sympathetic with the 

 trigeminus and facialis. 



t Cp. the elaborate work recently published by Max Fiirbringer ("Fest- 

 schrift fiir C. Gegenbaur," Bd. iii.) 



