228 ME. W. K. PAEKEE ON THE STEUCTUEE AND DEVELOPMENT 



With regard to the Amphibia, however, there are some points which I have lately 

 discovered that are of great importance. 



As to the abortion of the upper part of the suspensorium in the Selachians, in such 

 contrast ^ith its trifurcate condition in the Urodeles, and its bifurcate condition in the 

 Batrachia, I tind myself, even in details, in the happiest conformity of views with 

 Professor Huxley. 



As to Cestracion (Huxley, 4, p. 42, fig. 6), I quite agree with him that the spiracular 

 cartilage is the separate " otic process" {ot.])); and it is worthy of notice that whilst 

 the spiracular cartilages of the Sharks are mere rays, yet they are chondrified detach- 

 ments of the thin edge of the tissue that fiUs the primary fold in front of the 

 first cleft. 



In the Batrachia the anmdus tympanicus is a cartilage ; and at first, in the Tadpole, 

 it is a process from the angle of the suspensorium ; it becomes then a free ray, and 

 then curves to form the tympanic ring — the analogue but not the homologue of the 

 " annulus " of Man and the other Mammalia. 



In some Urodeles this cartilage reappears, and in them forms an attachment to the 

 stapes alove the seventh nerve, or portio dura ; this is seen in Menopoina, Spelerpes, 

 Desmognathus. It imitates the " columella," but is not that organ, only a curiously 

 specialized homologue of the spiracular cartilage of the Shark and the annulus of 

 the Frog. 



As to the rudiments of the pedicle and otic process seen in some Selachians, I quite 

 agree with Professor Huxley, who shows both in an embryo of Notidamus cinereus 

 (4, p. 44, fig. 9, p.st.p). 



Gegenbaur {op. cit.), in his exquisite figures, shows these processes, notably in 

 Hexanchus and Ileptanclms (pi. 10. figs. 1, 2, 2', p) ; but they are very evident in 

 Scymnus and Sqtmtina (pi. 11. figs. 1, 2), and are still more clear in Centrophorus 

 (pi. 12, fig. 1). 



I am also quite satisfied, from the study of a large number of Amphibian skulls 

 (larval and adult), that the " pedicle " is the true primary head or apex of the sus- 

 pensorium. 



There are some curious points in the structure of the palatal bars worthy of note. 



Gegenbaur [op. cit. pi. 11. fig. 1, pi) figures in Scymnus a keystone piece to the 

 pterygo-quadrate bars in front. In certain birds, especially the Picidse, the two 

 palatine bones are united by a tract of thin cartilage, which ossifies as a medio-palatine 

 bone (Trans. Linn. Soc. ser. 2, vol. i. pi. 3, m.pa). 



I spoke of the absence of a " pharyngo-pleural " element in the upper mandibular 

 segment of the Selachians ; I have described such a cartilage attached to the fore end 

 of the pterygo-quadrate in a young specimen of the Aoxolotl {Siredon). A similar 

 cartilage is very constant in the palate of Passerine birds (" ^■Egithognathse," part i. 

 pi. 55. figs. 1, 13, t.pa); but this, in both cases, may belong to the " antorbital." 



