y 
ON THE VERTEBRATE SKELETON. 217 
M. Dugés, who has accurately figured the ‘cranio-facial’ cartilage of a 
gadoid fish in pl. ii. of his valuable Monograph*, gives as accurate a figure 
of the same cartilage in the Rana viridis (pl. 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 (15 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 
cireumscribe 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- 
ture+.’ 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, 14) resulting from this modification, “ Je ne 
Yai pas trouvé divisé, méme dans des individus trés-jeunes qui avoient encore 
un grand espace membraneux entre les 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 connation{ 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 
(io, 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 sphénoide sans ailes tempo- 
rales ni orbitaires ;’ the true and distinct ‘alisphenoid’ (6, fig. 13), with its 
typical connections and nerve-perforations (¢r), being described as the pe- 
* Recherches sur l’Ostéologie, &c. des Batraciens, 4to, 1835. : 
+ 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. Comp. i. (1800) p. 332. 
_ £ L 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 
