ON THE VERTEBRATE SKELETON. 205 
these reptiles, and preserves with singular constancy its normal relative po- 
sition anterior to the exoccipital, superior to and supporting the tympanic, 
and anterior to the squamosal when this is present. In lizards the mastoid 
is much reduced in size: in serpents it attains a considerable length. In the 
python and most serpents it forms no part of the proper wall of the cranium, 
but overlaps the contiguous parts of the parietal, alisphenoid, supra-occipital, 
and exoccipital, projecting backwards beyond the latter. It is large in the 
serpentiform batrachia, but presents in Cecilia (Cuvier, Régne Animal, 1817, 
pl. 6. figs. 1 & 2, g) its normal connections with the occipital (f), parietal 
(e), tympanic (#), and also with the post-frontal, which has coalesced or is 
connate with the frontal (at d, l.c.). Cuvier does not admit of this conflu- 
ence in the cecilia; and although he assigns the character ‘ point des fron- 
taux postérieures’ to the typical batrachia*, gives the name ‘ posterior frontal’ 
with a note of doubt, indeed, to g, and assigns to the bone h, which suspends 
the mandible, the name of “mastoidiens et caisses réunist.’ There is no 
actual necessity for assuming so rare a confluence to characterize the cecilia. 
The mastoid exists with all its normal connections, and beautifully manifests 
by its independence and large size the affinity of the cecilia to the true 
ophidia. In the typical batrachia, where the cranium is remarkably cha- 
racterized by instances of confluence which seem borrowed from the warm- 
blooded classes, the mastoid sometimes loses its independence, and appears 
as an exogenous process from the external and posterior part of the parietal, 
retaining however its normal office of suspending the tympanic : but in a skull 
of the Rana boans now before me, the suture between the mastoid (fig. 13, s) 
and parietal (7) is not obliterated, and it further articulates with the exocci- 
pital (:) behind and the alisphenoid (6) in front. Cuvier, in his description of 
the tympanic of the Rana esculentat, says,.that its upper branch articulates 
with the ‘rocher.. In Rana boans that branch articulates exclusively with 
the truncated extremity of the broad outstanding mastoid, which mastoid 
overhangs, as in all fishes, the petrosal, which is chiefly cartilaginous in the 
Rana boans (ib. 16). In Rana esculenta the mastoid (Dugés, Recherches 
sur les Batrachiens, fig. 1, 12) appears to have coalesced with the alisphenoid 
(ib. figs. 2, 6 & 7,12); and the compound bone has received the name of 
‘rocher’ from Cuvier and that of ‘rupéo-ptéreal’ from Dugés. The fora- 
men ovale however marks the alisphenoidal part (a distinct bone in my Rana 
bvans), and the suspension of the tympanic marks the mastoid, which, with 
its other connections, overhangs also in Rana viridis that mass of cartilage§ 
which immediately invests the membranous labyrinth and forms the ‘fenestra 
ovalis’ against which the plate of the columelliform stapes is applied. 
Prof. J. Muller has well recognized the homologue of this sense capsule in 
the Cecilia hypocyanea, in which he describes it as “ petrosum cum operculo 
fenestree ovalis||.” It is situated further back than in Rana, and appears poste- 
rior to the tympanic (7) and the large suspending mastoid (/), to which Muller 
gives the name of ‘temporale.’ In the singularly modified cranium of the 
Lythlops the mastoid articulates above with the parietal and supraoccipital, 
behind with the exoccipital, coalesces in front with the alisphenoid, as in 
some batrachia, and affords the usual articulation below to the tympanic. 
_ How necessary it is to retain a clear and consistent appreciation of these evi- 
* Ossem. Fossiles, v. pt. i. p. 386. + Régne Animal, ed. 1817, t. iv. p. 102. 
Ossem. Fossiles v. pt. ii. p. 390. 
§ The precocious development of this capsule in the larva of the frog is well shown by 
Reichert, ‘ Entwickelungsgeschichte des Kopfes,’ 4to, pl. i. figs. 13—15, x: it resembles 
that in the myxinoids and lampreys. : 
|| Beitrage zur Anatomie der Amphibien; Tiedemann’s Zeitschrift fiir Physiologie, 
Bd. iy. 1831, p. 218, pl. 18. fig. v. &. 
