On the archetype and homologies of the vertebrate skeleton / by Richard Owen.

  • Richard Owen
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: On the archetype and homologies of the vertebrate skeleton / by Richard Owen. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    king part, by its large size, in the formation of both the internal and ex- riiaf surfaces of the cranial* box, which size depends essentially on the •gree of development of the frontals, parietals and occipitals: it is further •ged that the suborbitals (‘apophyse jugule’) are likewise attached to it; that e preopercular(‘apophyse styloi'de’) diverges, and is directed or abuts against ; that, finally, the bone in i[uestion (no. s, fig. 5) is, with the exception of the •trosal, the sole part of tlie temporal bone which takes a direct part in e formation of the cranial box. “ D’apres ces considerations,” M. Agassiz .•oceeds, “il est impossible de prendre I’os No. 12 [no. s, in fig. 5], que uvier a nomine mastdidien, pour autre chose que pour la veritable ecaille du niporal. II prend part a la formation de la boite cerebrale, il donne inser- jii a I’arcade zygomatique, enfin, il prete une articulation au preopercule, le nous regardons maintenant comme le veritable representant de I’apo- ivse stylouie du temporal,” 1. c. p. 63. Admitting, for the sake of the argu- e'nt, that the preopercular is the homologue of the stylohyal, and that it arti- ilates with the so-called ‘ ecaille du temporal,’ which is not the case in the ajority of fishes, yet this would prove more for the ‘mastoid’ than for the Kjuamosal’ character of no. s, fig. 5. The stylohyal unquestionably articu- tes in many mammals with the mastoid or petromastoid, between which id the tympanic it is anchylosed in man, and it rests with M. Agassiz to nnonstrate the species in which it articulates with the true squamous part •'the temporalf. ■ With regard to the connection with the suborbital chain of ossicles, which I. Agassiz regards, with Geoftroy, as the jugal or zygomatic arch, even • idmitting such connection to be the rule and not the exception, all its ^^ce as an argument in favour of the squamosal character of no. s Avill spend on the ultimate decision of comparative anatomists as to the respect- -'e claims of the upper and lower zygomata in the macaw’s skull, for ixample (pi. 1, fig. 1), to a special homology with the zygomatic arch in jan and other mammals. The orbit in the bird cited, as in other Psit- •ddcE, is circumscribed below by a bony frame continued from the lacrymal •3) to the postfrontal (12), and thence to the bone (a) which I regard as le mastoid. Below this frame, the slender bone, considered by Cuvier as ■je jugal, and by me as the coalesced jugal (20) and squamosal (27), extends 'em the maxillary (21) backwards to the tympanic (2s), and forms a second *ch or zygoma. According to the Cuvierian and generally-received view of 1 i-ie homology of no. s in the bird, the bridge which it sends forward over the ?mporal fossa to join the above-described inferior boundary of the orbit, I the macaw, would be the zygomatic process; and that boundary would be •hat M. Agassiz calls its homologue in fishes, viz. the jugal or ‘arcade zygo- oatique.’ But what then is the parallel zygomatic arch below(2o, 27), con- 4iany fishes of different grades of organization, and by some, as the sturgeons and siluroids, g. under a scattered arrangement, more like that in the crocodiles than is seen in the scale mnour of the typical ganoids, it might have some weight in proving the affinity of such ' anoids to the highest order of reptilia; but, viewing this character under all its relations, am not disposed to regard it as establishing that affinity more directly, than it would the : ffinity of the crocodile to the mammalian genus Dasgpus. It is for the reasons above assigned nat I have been accustomed to treat, in my Lectures, of the anatomical characters of the roup represented by the Polypterun and Lepidosteus, as those of a Salamandroid, rather than f a Saurr/id family of fishes; the characters being carried out in the direction of the batra- hian order by the remarkable genera Prolopterns and Lejndoairen. * .More properly ‘ otocranial,’ in Icpidostcus at least. t In my notes on the osteology of Mammalia, I find that the stylohyal sometimes articu- ates with the petrosal, sometimes with the mastoid, exclusively, as in most mammals, ometimes with the tympanic, sometimes with the paroceipitjd process ; but no instance is ecorded of its articulation with the srjuamous portion of the temporal.