ORAL CIRRI OF SILUROIDS AND ORIGIN OF THE HEAD IN VERTEBRATES. 19 



capsule, and indeed Gegenbaur concludes that it is a portion cut off from 

 the cranium. That, however, is controverted by comparison outside 

 the Selachii. In the Dipnoi there is a trelliswork of cartilage forming 

 the wall of the olfactory capsule and, in view of the frequent fusion of 

 the nasal labial with the cranium in Selachii, this trelliswork may 

 perhaps be held to represent a nasal labial. 



The nasal capsule and tube of Myxine is surrounded by irregular 

 rings of precartilage, which represent the nasal labials. Gegenbaur, in 

 mentioning this view, concludes that it is a hasty one, but all doubt 

 seems to be removed by the fact that the nasal tube is worked by a 

 muscle, the Nasalis of Fiirbringer or " Zuriickzieher der Nasenoffnung " 

 of Miiller, which belongs to the tentacular system and is supplied by 

 the Ophthalmicus profundus, while the nasal tube itself receives 

 sensory branches from the Ophthalmicus profundus. The compressor 

 narium M. ethmoideonasalis R, and a portion of the trans versus oris 

 F. are also attached to the nasal tube. 



On this point Miiller remarks that "Since two olfactory nerves 

 proceed into the single olfactory capsule, the single olfactory capsule is 

 to be explained rather by the apposition than fusion of the nasal 

 capsules of cartilaginous tish, and this happens indisputably through 

 the suppression of those parts which otherwise lie between the nasal 

 capsules". While agreeing with Miiller in principle, I regard the 

 supporting elements of the nasal capsule of Myxine as corresponding 

 only to the nasal labial of Selachii, not to the whole capsule. 



Furthermore no one, who has examined a series of sections of the 

 head of Myxine, can doubt that the plate supporting the posterior part 

 of the nasal or hypophysial tube where it opens into the palate, the 

 " Gaumenplatte " of Miiller or "posterior intertrabecula " of Parker is 

 a posterior continuation of the nasal skeleton, and as such ultimately 

 to be derived from a nasal tentacle. 



Miiller compared the nasal cartilages of Chimaera with the rings of 

 the nasal tube of Myxine. This view is shown below to be untenable. 

 Only the most anterior crescentic cartilage (/of Miiller) corresponds 

 to the nasal labial of Selachii and the nasal rings of Myxine. 



Nerve Supply. 

 The motor nerves, which have occasionally to be referred to in this 

 paper as supplying the system of tentacular muscles, are, to follow the 



