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. 8, 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'apres ces considerations," M. Agassiz 

 proceeds, " il est impossible de prendre l'os No. 12 [no. s, in fig. 5], que 

 Cuvier a nomme masto'idien, pour autre chose que pour la veritable ecaille du 

 temporal. II prend part a la formation de la boite cerebrale, il donne inser- 

 tion a l'arcade zygomatique, enfin, il prete une articulation au preopercule, 

 que nous regardons maintenant comme le veritable representant de l'apo- 

 physe styloide du temporal," I. 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 ' ecaille 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 temporal f. 



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 Psittacidce, is circum- 

 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 (2c) and squamosal (27, fig. 23), extends from 

 the maxillary (21) backwards to the tympanic (2s), and forms a second arch 

 or zygoma. 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. 



f 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. 



