CEANIAL NERVES OF CHIMERA MONSTROSA. 661 



dorsal end of the hyomandibular cleft, and then downwards a short distance along the 

 mandibular arch " (italics mine). There is here very little evidence in favour of prse- 

 spiracular gill clefts. Again, in the mammalian facial, the post-spiracular, as usual, is 

 developed first ; whilst, later on, the prse-spiracular is given off from the oral side of the 

 facial ganglion in front of the hyomandibular cleft, extends downwards, and enters into 

 branchial relations with the mandibular arch. These facts show that it is the prse- 

 spiracular, and not the post-spiracular, the peripheral distribution of which corresponds 

 to that of the chorda tympani. Unfortunately, the early development of the latter is, 

 I believe, not known in Mammals ; but, according to my view, it should be formed 

 from the prse-spiracular nerve of the embryo. 



I have thus endeavoured to show that whilst the chorda tympani was correctly 

 homologised by Strong and Pinkus, yet both these observers failed to recognise in it 

 the prse-spiracular nerve of cartilaginous fishes ; and further, that the internal man- 

 dibular nerve of Strong is not the internal mandibular hitherto described in Selachians. 

 The latter is simply the ventral continuation on to the pharynx ( = mostly splanchnic 

 motor fibres) of the post-branchial division of the facial, and, as such, does not fulfil the 

 requirements of any definition of a homologue of the chorda tympani. In no Selachian 

 is the internal mandibular known to consist of splanchnic sensory fibres, nor does it 

 ever enter into branchial relations with the mandibular arch (cp. quotation from Ewart 

 above). Strong bases his homology of the chorda in Amphibia on three facts, which he 

 says are common both to amphibia and man : — 



(1) Both have the same internal origin, i.e., from the ' fasciculus communis.' 



This is " essentially the central origin of the branchial [visceral sensory 

 (and motor ?)] nerve supply." 



(2) Both have the same kind of fibres. 



(3) Both have the same course and final termination. With regard to the lingual 



branches, Strong discovered that the chorda of larval amphibia innervated 

 the pharynx " in the same transverse plane as the location of the future 

 tongue " (cp. Chimsera). He also examined adult forms, and found that 

 on the development of the tongue the chorda tympani passed on to and 

 partly supplied it. 



Kamsay Wright (34) controverts Van Wijhe's statement that the ramus oticus of 

 Ganoids is a branch of the Vth, and his proof that it is a facial branch in Lepidosteus 

 and Amia brings the Ganoids into my scheme of the lateral line system. He further 

 shows that the spiracular demi-branch or opercular gill of Lepidosteus is innervated both 

 by the Vllth and IXth cranial nerves, and hence = the spiracular demi-branch + the 

 hyoidean demi-branch of other fishes. The portion innervated by the IXth is not 

 respiratory, and therefore forms the pseudobranch, whilst the hyomandibular cleft has 

 no external opening. It is- with regret that one adds that this arrangement cannot 

 be said to hold good for Chimsera. 



