ae 
—— 
; 
4 
ON THE VERTEBRATE SKELETON. 207 
The high repute which M. Agassiz has so justly earned in ichthyotomy 
renders the accession of his name in support of Drs. Hallmann, Reichert, 
and Kostlin’s determination of the bone in question, one to which those able 
homologists and their followers will naturally attach great weight, and which 
indeed has caused me to pause and retrace more than once, and with the 
utmost pains and care, every step in the series of comparisons which have 
finally brought conviction of the accuracy of the Cuvierian determination of 
no.s in fishes. 
- I am not aware that any anatomist has replied to the objections to the 
Cuvierian view propounded by M. Agassiz. Drs. Hallmann and Kostlin, 
who have published the most elaborate monographs on the temporal and 
other bones of the skull since the time of Cuvier, concur entirely with the 
~ learned Swiss naturalist. Dr. Reichert, in giving the name of ‘squama tem- 
poralis’ to no. s, and that of ‘processus temporalis posterior’ to its process, 
transfers the name ‘ processus mastoideus’ to the paroccipital (no. 4, fig. 5)*. 
It becomes then necessary to consider the arguments of M. Agassiz in favour 
of the homology of no. s. in fishes with the squamosal no. 27 in mammals. 
In the valuable monograph on the osteology of the pike (/sox) in the 15th 
‘Livraison’ of the ‘Recherches sur les Poissons Fossiles,’ the author says 
(p. 66), “ Un os de la téte placé entre le frontal postérieur, le frontal prin- 
cipal, le pariétal, la grand aile sphénoidale et l’occipital latéral, ne saurait 
jamais étre envisagé comme correspondant a l’apophyse mastoidienne du 
temporal. D’aprés ses liaisons, je crois donc qu'il faut envisager le mastoidien 
de Cuvier comme l’analogue de I’ écaille du temporal ou comme le temporal 
proprement dit. C’était déja l’opinion de Spix, qui est tombé juste sur ce 
_ point.” To this I reply that, in regard to the connections of the mastoid, those 
with the parietal, alisphenoid and exoccipital, are more constant than that 
with the frontal, which is interrupted in mammalia by the interposition of 
the expanded squamosal, peculiar to that class; but the mastoid retains its 
piscine connection with the postfrontal in many reptiles and some birds. On 
the other hand, the union of the squamosal with the frontal is by no means 
a constant character in mammalia: it is rarely found in the orang, still more 
rarely in man, never in the cetacea and monotremes, nor in certain ruminants, 
nor in the myrmecophaga, &c. The connection of the mastoid with the 
frontal is more common than is the connection of the squamosal with the 
exoccipital. It is a bold leap to take from the mammal to the fish in the de- 
termination of a variable bone like the squamosal: nevertheless, | would re- 
quest the unbiassed reader to glance at fig. 12, whilst he reads M. Agassiz’s 
précis of the character of the squamosal above cited, and see how far no. s de- 
viates from it, save in regard to the frontal connection. Spix, who appears 
not to have traced the beautiful gradation of the mastoid in the mammalia, 
and who was unacquainted with the decisive step to its normal condition in 
the oviparous vertebrates made by the monotremes,—and who was influenced, 
therefore, by seeing that bone in higher mammals pushed back from any con- 
nection with the alisphenoid and postfrontal by the interposed squamosal, 
which usurps these connections and combines them with others, as with the 
parietal and tympanic, which the mastoid (no. s) presents in fishes,—not un- 
reasonably concluded that no. s represented the squamosal in that class; and 
it is probable that M. Agassiz, who received his anatomical rudiments at 
Munich, and was early engaged in describing the fishes collected in Brazil by 
the author of the ‘ Cephalogenesis,’ might have derived a bias in favour of this 
view which prevented his assigning their due value to the connection of no. s 
in fishes with the paroccipital, and its contribution to the otocranial cavity. 
* Op. cit. tab. iii. figs. 9 and 13, p, g. 
