ON THE VERTEBRATE SKELETON. 217 



M. Duges, who has accurately figured the ' cranio-facial' cartilage of a 

 gadoid fish in pi. ii. of his valuable Monograph*, gives as accurate a figure 

 of the same cartilage in the Rana viridis (pi. i. figs. 6, 7, of the same work), 

 out of which has been ossified a bone which transmits the olfactory nerve to 

 its sense-capsule: this bone (is in the figures cited) rests below upon the di- 

 vided vomer and on the end of the presphenoid, sustains above the nasal and 

 fore-part of the frontal, affords an articular surface on its outer part for the 

 palatine, and only fails to repeat every characteristic connection of the pre- 

 frontals in fishes, because (as likewise happens in certain of that class) there 

 is no lachrymal bone developed in the Batrachia. The sole modification 

 of any consequence tending to mask the homology is this ; that whereas we 

 find in many fishes ossification extending into the persistent part of the cra- 

 niofacial cartilage connecting, whilst it separates, the prefrontals, so as to 

 circumscribe the canals for the transmission of the olfactory nerves, such ossi- 

 fication proceeds in the anourous batrachia to anchylose the prefrontals with 

 each other, and convert them into a single bone. This difference however 

 sufficed with Cuvier to make of it a new and peculiar bone — an ' os en cein- 

 turef .' It would have been as reasonable to have given a new name to the 

 supraoccipital in the Lepidosteus, because it is divided in the middle line in- 

 stead of being single, or to the frontal in the species where it is single instead 

 of being divided, or to the vomer in the frog because it is double instead of 

 single, or to the exoccipitals in the same reptile, which manifest the same 

 mesial and annular confluence as the prefrontals. But, adds Cuvier, in refer- 

 ence to the single bone (fig. 13, u) resulting from this modification, " Je ne 

 l'ai pas trouve divise, meme dans des individus tres-jeunes qui avoient encore 

 un grand espace membraneux entreles os du dessus du crane." Nor did the 

 great anatomist ever find the rudiments of the radius and ulna distinct at any 

 period of development of the single bone of the Batrachia, which he never- 

 theless rightly describes as representing both bones of the fore-arm : nor 

 did he ever find a division of the single parietal in the embryo crocodile, 

 which he equally well recognized, nevertheless, as the homologue of the two 

 parietals, which in most fishes have been subject to greater modifications in 

 their connections and relative position than the single prefrontal presents in 

 the anourous batrachia. These are not the only instances where relations of 

 homology are by no means obscured, nor ought to be, by reason of the con- 

 fluence or even connationj of essentially distinct elements. The capsule of 

 the olfactory organ, partly protected by the anterior infundibular expansions 

 of the connate prefrontals, undergoes no partial ossification homologous with 

 the 'turbinal' (19, fig. 5) of fishes, but remains cartilaginous, like the scle- 

 rotal and petrosal. 



The prefrontals, however, are not only connate with each other in the 

 frog, but coalesce with the contiguous neurapophyses — the orbitosphenoids 

 (10, fig. 13). And this modification has led Cuvier, notwithstanding the 

 connection of the bone 10 with the presphenoid below, with the frontal 

 above, and with the prosencephalon, optic nerve (op) and orbit, to charac- 

 terise the batrachian skull as having " un seul sphenoide sans ailes tempo- 

 rales ni orbitaires;" the true and distinct ' alisphenoid ' (e, fig. 13), with its 

 typical connections and nerve-perforations (tr), being described as the pe- 



* Recherches sur l'Osteologie, &c. des Batraciens, 4to, 1835. 



t Ossemens Fossiles, 4to, t. v. pt. ii. p. 387. He had before applied the name of ' ceinture 

 osseuse ' to the scapular arch in fishes. — Lecons d' Anat. Conip. i. (1800) p. 332. 



+ I use these terms in the same definite sense as the botanists ; those essentially distinct 

 parts are connate which are not physically distinct at any stage of development, those united 

 parts are confluent which were originally distinct. 



1846. Q 



