CRANIAL NERVES OF CHIMERA MONSTROSA. 663 



Facial. 



(3) Dorsal from lobus ' trigeminus.' Primary dorsal root of embryo. = the lateral 

 line root, and is more or less connected witli all the lateral line roots. Before Marshall 

 and Spencer's paper, always described as belonging to the Vth. 



(4) Ventral. Secondary ventral root of embryo. In adult closely related to (2). = 

 facial proper root + the accompanying external mandibular. The latter, however, 

 usually leaves it and arises from (3). 



(5) Ventral. Development unknown. Always connected with (3). = remainder of 

 lateral line system not included in (3) and (4) (this may be a portion of either the 

 superficial ophthalmic or buccal). Found in Chimsera, Acipenser, and Lsemargus. May 

 be in front of (4), but is not so in Chimsera. Has been described as belonging to Vth. 

 Seems to be very often missing ; and when so, it is probably fused with (4), and hence 

 becomes related to (2). 



I have added root (5) principally because it is a very prominent root in Chimsera, 

 which, as far as I am aware, is the only fish in which the roots of the Vth and Vllth 

 remain perfectly distinct, and which, therefore, probably shows us the nerves in a primi- 

 tive condition. The nearest approach to Chimsera in this respect are the Pleuronectidse, 

 as first pointed out by Stannius. It is interesting to note that in Amphibia the Vth 

 arises by a single root, and only contains a few motor fibres (Strong). 



With regard to the unity of the lateral line system, which I have maintained above, 

 there is a considerable wealth of evidence showing that at least the superficial ophthalmic 

 and buccal cannot be divided into two nerves. Van Wijhe (31, p. 27) first showed 

 that these nerves arose by the splitting of a single trunk, and this observation was con- 

 firmed by Beard (35), who further stated that the supra- and infra- orbital canals arose 

 by the splitting of a single "branchial sense organ." Ewart (58, pp. 66 and 77) 

 favours the view that the superficial ophthalmic and buccal represent a single dichotomised 

 trunk, whilst Pollard (60) # showed that this was actually the adult condition in Clarias 

 and Auchenaspis. Pinkus (67) proved the same for Protopterus, and added the im- 

 portant observation that the common trunk communicated with the lateralis nerve. 

 Finally, Strong (68) established the fact that the lateral line nerves of Amphibia arose 

 by two roots, which had a common internal origin in the brain. 



I have previously referred to a nerve known as the ' recurrent facial.' It was first 

 discovered by Stannius in Silurus, but does not, as stated by him, occur in Chimsera. 

 Pollard figures and describes it in many species of Siluroids (60). It arises from the 

 Vllth portion of the fused Vth and Vllth ganglia, frequently anastomoses with a branch 

 of the lateralis, and in Clarias supplies the sensory canal " at the base of the dorsal 

 fin." Pollard's description of this important nerve is not as full and as clear as one 

 could wish, but it certainly has no representative either in cartilaginous fishes or in 



* This author makes the interesting statement that in Trichomyderus there are only two sense organs on the infra- 

 orbital canal, and hence the buccal nerve is much reduced, and represented only by two twigs. 



VOL. XXXVIII. PART III. (NO. 19). 4 Z 



