ON THE VERTEBRATE SKELETON. 205 



these reptiles, and preserves with singular constancy its normal relative po- 

 sition anterior to the exoccipilal, 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 Ccecilia (Cuvier, Regne Animal, 1817, 

 pi. 6. figs. 1 & 2, g) its normal connections with the occipital (/), parietal 

 (e), tympanic (h), and also with the post-frontal, which has coalesced or is 

 connate with the frontal (at d, 1. c). Cuvier does not admit of this conflu- 

 ence in the cascilia; and although he assigns the character 'point des fron- 

 taux posterieures' 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 " mastoi'diens et caisses reunisf." There is no 

 actual necessity for assuming so rare a confluence to characterize the cagcilia. 

 The mastoid exists with all its normal connections, and beautifully manifests 

 by its independence and large size the affinity of the csecilia 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 liana 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 (a) behind and the alisphenoid (e) in front. Cuvier, in his description of 

 the tympanic of the Rana esculenta\, 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. 10). In Rana esculenta the mastoid (Duges, 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 ' rupeo-ptereal ' from Duges. The fora- 

 men ovale however marks the alisphenoidal part (a distinct bone in my Rana 

 boans), 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 Ccecilia hypocyanea, in which he describes it as " petrosum cum operculo 

 fenestra? ovalis ||." It is situated further back than in Rana, and appears poste- 

 rior to the tympanic (i) and the large suspending mastoid (Ji), to which Muller 

 gives the name of ' temporale.' In the singularly modified cranium of the 

 Tythlops 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. f Regne 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, pi. i. figs. 13 — 15, x : it resembles 

 that in the myxinoids and lampreys. 



|| Beitrage zur Anatomie der Amphibien ; Tiedemann's Zeitschrift fiir Phvsiologie, 

 Bd. iv. 1831, p. 218, pi. 18. fig. v. k. 



