1876.] 



the Skull in the Urodelous Amphibia. 



335 



The difficulfcy with regard to the existence of another preoral arch is now 

 settled; the so-called " ant orbital " cartilage o£ Urodeles is a distinct 

 ethmo-palatine rudiment of a visceral arch, and crops up in several 

 groups ; the pterygoid foregrowth of the suspensoriuni is another thing, 

 a symj^lectic process, and not an independent arch. 



The Urodeles differ from the Batrachia in having an " ascending 

 process " to their suspensorial " pedicle ; " only in Proteus is this absent, 

 because only in this type does the trabecula fail to send upwards an ali- 

 sphenoidal crest. 



Late or earli/, the Batrachia never fail to develop an epihyal (hyo- 

 mandibular) segment, and this is always specialized to form the " colu- 

 mella auris." 



Proteus develops a large, and Siren and Menopoma a small, cartilage of 

 this nature : it is never specialized into a columella, however, in them. 

 In twelve other kinds (" Caducibranchs ") I have failed to find a rudiment 

 of this segment. 



In the Batrachia, as I have shown (the fact was first pointed out to 

 me by Professor Huxley), the stapes develops in the fenestral cleft as an 

 independent cartilage. 



In the Salamandrians, as I long ago asserted, the stapes is segmented 

 off from the pre-existing cartilage of the fioor of the periotic capsule. I 

 erred in supposing the frog's stapes to be formed in the same way. 



In the Batrachia, as I correctly showed in my first paper, a ray from 

 the elbow of the suspensorium becomes detached, to form part of the 

 external auditory apparatus ; not, however, the " columella," as I sup- 

 posed, but the cartilaginous annulus tympanicus. 



That ring of cartilage I correctly referred to the category of " bran- 

 chial rays," such as are seen in the Selachians : it is, in truth, their 

 spiracular cartilage (that of the sharks, not that of the skates, which is a 

 free metapterygoid segment). 



As a rule, in the Urodeles, there is a suspensorio-stapedial ligment run- 

 ning forwards heneatli the " portio dura " nerve ; in my chief instance, the 

 Axolotl, there is, instead of this, a fascia passing over that nerve to the 

 place of the spiracular ray of the tadpole, namely, the back of the sus- 

 pensorium above. 



In the huge Menopome, which partly loses its gills, and in certain 

 small true Caducibranchs (namely, Spelerpes salmonea, S. ruhra, Desmo- 

 gnathus fuscus) there is a recurrence of the spiracular cartilage over the 

 portio dura. 



This generally attaches its small posterior end to the face of the stapes, 

 and then is encupped by the stapedial ossification : on one side of Des- 

 moynathus it does this, and on the other it is distinctly ossified, and not 

 fixed to the stapes. 



This succedaneura for the true columella is very large in the Meno- 

 pome : it is a thick but somewhat flattened cartilage, in outline like a 



VOL. XXV. 2 B 



