ON THE VERTEBRATE SKELETON.” 209 
taking part, by its large size, in the formation of both the internal and ex- 
ternal surfaces of the cranial* box, which size depends essentially on the 
degree of development of the frontals, parietals and occipitals: it is further 
urged that the suborbitals (‘apophyse jugale’) are likewise attached to it; that 
the preopercular(‘apophyse styloide’) diverges, and is directed or abuts against 
it; that, finally, the bone in question (no. s, fig. 5) is, with the exception of the 
petrosal, the sole part of the temporal bone which takes a direct part in 
the formation of the cranial box. ‘“ D’aprés ces considérations,” M. Agassiz 
proceeds, “il est impossible de prendre l’os No. 12 [no.s, in fig. 5], que 
Cuvier a nommé mastoidien, pour autre chose que pour la véritable écaille du 
temporal. Il prend part a la formation de la boite cérébrale, il donne inser- 
tion 4 l’areade zygomatique, enfin, il préte une articulation au préopercule, 
que nous regardons maintenant comme le véritable représentant de l’apo- 
physe styloide du temporal,” /. c. p.63. Admitting, for the sake of the argu- 
ment, that the preopercular is the homologue of the stylohyal, and that it arti- 
culates with the so-called ‘ écaille du temporal,’ which is not the case in the 
majority of fishes, yet this would prove more for the ‘mastoid’ than for the 
‘ squamosal’ character of no. s, fig.5. The stylohyal unquestionably articu- 
lates in many mammals with the mastoid or petromastoid, between which 
and the tympanic it is anchylosed in man, and it rests with M. Agassiz to 
demonstrate the species in which it articulates with the true squamous part 
of the temporalt. 
With regard to the connection with the suborbital chain of ossicles, which 
M. Agassiz regards, with Geoffroy, as the jugal or zygomatic arch, even 
admitting such connection to be the rule and not the exception, all its 
force as an argument in favour of the squamosal character of no. s will 
depend on the ultimate decision of comparative anatomists as to the respect- 
ive claims of the upper and lower zygomata in the macaw’s skull, for 
example, to a special homology with the zygomatic arch in man and other 
mammals. The orbit in the bird cited, as in other Pstttacide, is cireum- 
scribed below by a bony frame continued from the lacrymal to the post- 
frontal, and thence to the bone (no. s) which I regard as the mastoid. 
Below this frame, the slender bone, considered by Cuvier as the jugal, and 
by me as the coalesced jugal (26) and squamosal (27, fig. 23), extends from 
the maxillary (21) backwards to the tympanic (2s), and forms a second arch 
orzygoma. According to the Cuvierian and generally-received view of the 
homology of no.s in the bird, the bridge which it sends forward over the 
temporal fossa to join the above-described inferior boundary of the orbit, 
in the macaw, would be the zygomatic process; and that boundary would be 
what M. Agassiz calls its homologue in fishes, viz. the jugal or ‘arcade zygo- 
matique. But what then is the parallel zygomatic arch below, connecting 
Many fishes of different grades of organization, and by some, as the sturgeons and siluroids, 
e. g. under a scattered arrangement, more like that in the crocodiles than is seen in the scale 
armour of the typical ganoids, it might have some weight in proving the affinity of such 
ganoids to the highest order of reptilia; but, viewing this character under all its relations, 
I am not disposed to regard it as establishing that affinity more directly, than it would the 
affinity of the crocodile to the mammalian genus Dasypus. It is for the reasons above assigned 
that I have been accustomed to treat, in my Lectures, of the anatomical characters of the 
group represented by the Polypterus and Lepidosteus, as those of a Salamandroid, rather than 
of a Sauroid family of fishes; the characters being carried out in the direction of the batra- 
chian order by the remarkable genera Protopterus and Lepidosiren. 
* More properly ‘ otocranial,’ in lepidosteus at least. 
+ In my notes on the osteology of Mammalia, I find that the stylohyal sometimes articu- 
lates with the petrosal, sometimes with the mastoid, exclusively, as in most mammals, 
sometimes with the tympanic, sometimes with the paroccipital process: but no instance is 
recorded of its articulation with the squamous portion of the temporal. 
