228 MR. W. K. PARKER ON THE STRUCTURE 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 with its trifurcate condition in the Urodeles, and its bifurcate condition in the 
Batrachia, I find 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” (o¢.p); 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 fills the primary fold in front of the 
first cleft. 
In the Batrachia the annulus 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 above the seventh nerve, or portio dura; this is seen in Menopoma, 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 Heptanchus (pl. 10. figs. 1, 2, 2', p); but they are very evident in 
Scymnus and Squatina (pl. 11. figs. 1, 2), and are still more clear in Centrophorus 
(pie tafe. 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. pl. 11. fig. 1, p) figures in Scymnus a keystone piece to the 
pterygo-quadrate bars in front. In certain birds, especially the Picide, the two 
palatine bones are united by a tract of thin cartilage, which ossifies as a medio-palatine 
bone (Trans. Linn. Soe. ser. 2, vol. i. pl. 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 (‘‘ AZgithognathe,” part i. 
pl. 55. figs. 1, 13, ¢.pa); but this, in both cases, may belong to the “ antorbital.” 
