On the archetype and homologies of the vertebrate skeleton / by Richard Owen.
- Richard Owen
- Date:
- 1848
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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![necting the maxillary with the tympanic, and marked z*' in fig. 7, taf. i. of 1 Hallmann’s monograph ? If Cuvier had been correct in regarding no. 8 asi squamosal, the name ‘ jugal’ ought to have been transferred from the loi zygoma to the upper one (pl.l, fig. 1, 73) connected with such squamosal the macaw : and with a like consistency the name ‘jugal’ ought to have bi> retained for the siiborbital chain of dermal bones in fishes (pi. 1, fig. 2, 73)! which it had been applied by Geoffroy St. Hilaire, and to which it has bi> restored by M. Agassiz. But, in truth, there may be clearly discerned in beautiful modification which has been adduced from the PsittacidcB, a prri of Cuvier’s erroneous homology of the bone no. 8 in the class of birds, andj the same time of his accurate homology of tlie same bone in tliat of fishes Is there no significance in the fact of the bone anterior to the orbit, whi| we call lacrymal in man down to the lowest reptile, being constantly p « forated by a mucous duct ? Can we not recognize in this function a- glandular relation, as in the commonly thin scale-like character of that boi j and its connections in front of the orbit, the repetition of the characters- the largest, most anterior, and most constant of the suborbitals in fishes (7i.73j| If the rest of that chain be sometimes wanting, but more commonly prese in that class ; if it should present the condition occasionally of a strong coni nuous bony inverted arch, spanning the orbit below from prefrontal to posl frontal, as in the right orbit of the Hip2)oglussus and the left orbit of Rhombh ought we to lose our grasp of the guiding thread of ‘ connections’ by beii< confronted with a repetition of that condition in the skulls of certain hire caused by a continuous ossification from the lacrymal to the post-fronttJ seeing that a diverging bony appendage of the maxillary arch, unknown in til class of fishes, has there established a second and true ‘zygoma’ below til suborbital one ? The extension of the ossification from the post-frontal cni of the suborbital arch to the mastoid is, in truth, a beautiful repetition of ai ichthyic cranial character, not unknown however in the reptilia; and whilil it adds a proof of the mastoidal character of no. s in the bird, it reflecif reciprocal confirmation of the accuracy of Cuvier’s determination of tlu bone in fishes. The true signification and homologies of the bones in that interestinil class could never have been elicited from an exclusive study of it, howevel extensive, detailed or profound ; nor will the feeble rays reflected from am! thropotoniical reminiscences lend sufficient light in their determination : the-I can be clearly discerned only by the full illumination of the beams conceni trated from all the grades of organic structure. M. Agassiz, descending tc| the determination of the squamosal in fishes from its characters in man, conJ eludes that it must be the bone no. s, fig. 5, because that bone takes part ill the formation of the inner as well as the outer walls of the cranial cavity. Buf this protective function is an exceptional one in the squamosal (fig. 6, 27)*| it is peculiar to that bone only in one class, and, as we have seen, is not con- stant even there ; whilst, on the other hand, the mastoid is recognizabhl from the inner surface of the cranial walls of the highest mammal (in theJ human cranium where it is impressed with the fossa sigmoidea, fig. 6, s), and] in a still greater degree in that of the lowest mammal {Echidna, fig. 12, 3) ;| whilst in almost every mammal, by its coalescence with the outer surface of I the petrosal, it closely repeats the protective character in relation to the ex- ternal semicircular canal, which it presents in fishes,—a function which is] altogether foreign to the squamosal in every mammal. I have dwelt thus! long, perhaps tediously, and it may be thought unnecessarily, on the true; characters and homologies of the petrosal and mastoid, because their determi-■ nation is essential to, and, indeed, involves that of the squamosal and otheri](https://iiif.wellcomecollection.org/image/b21307830_0054.jp2/full/800%2C/0/default.jpg)
