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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    its of resemblance between tlie jirefrontals of the crocodile aiul those of fish are the mesial approximation and junction of their descending (neu- 1 ophysial or rhinencephalic) plates—the most constant aiul important parts j he bones in question. i f the frontal of the ruminant or other mammal were expanded only at j parts corresponding with the detached bones called “ Irontaux ante- ■ in the crocodile, there might then be a primd fade probability that l) .res connate ‘D parts, dismembered in the crocodile’s skull. jj 1 expansions were *1 the vastly increased lateral as well as anteroposterior development, and highest j more or less vertical convex expansion of tlie frontal in the ^ ebrate class, naturally indicate, in the first place, an inquiry into the ^ :;oraitant modification of the nervous centres by which the development hat bone is mainly governed; and if such modification should then be ] id to exist, in the cerebrum, for example, which, from the ascertained , elative progress of the frontal in other classes, ought to cause or be ^ dated with such a general development of that bone as characterises the 1 in the mammalian class, it must surely be superfluous and gratuitous '.xplain that development by the hypothesis of a coalescence of another :ntiallv distinct element of the cranial parietes: especially if that element roved, by a similar tracing of its relations to the progressive development he cerebral centres, to have as essential and exclusive a dependence 1 the rhinencephalon as the frontal bone has upon the prosencephalon, he position of the upper peripheral part of the prefrontal in the situation . hich it is seen in the crocodile, is, in fact, the least constant and import- of the characters of that bone. In the bull-frog, for example, the ex- -d part of the prefrontal is mesiad of the conjoined parts of the nasals frontals instead of being lateral; in the sword-fish the prefrontals barely jar, and in the python they do not appear at all, upon the upper surface Lae skull; but they retain in each their more typical neurapophysial po- Ln, with all their more constant and essential characters. The enormously loped frontal of the mammal masks these characters, and usurps the ■constant and least important one, viz. superficial position, on which alone *ier insists as proving the prefrontal of the crocodile, with its complex j|;:tions and connections, to be such a dismemberment of the true frontals le ruminant, as may be marked oif with the pen on the upper surface of ifrskull I j he descending [rhinencephalic] plates of the prefrontal in the crocodile 9, u) are subcompressed in the axis of the skull, and expanded laterally, ^cially at their upper part; where, in the alligator, I find them forming a # 'Ow cup, concave forwards for the lodgment of the cartilaginous olfactory # .ule,—of that part, namely, which is ossified in mammalia, and there de- f into the great labyrinth of the superior turbinals and ethmoidal cells. 4 vertical plates, continued forwards from the prefrontals, which extend r 'eto the nasal suture and descend into the vomerine groove below, to aid 1 rraing the ‘septum narium,’ are cartilaginous in the crocodile; they are > ? or less ossified, and form the ‘lamina perpendicularis ethmoidei’ in 1 imals. The median plate, dividing the olfactory nerves at their exit, and ' doped backwards as a partial septum of the rhinencephalic chamber of i cranium, and continued into the simple interorbital septum of the croco- ' also remains cartilaginous: when ossified in mammals, it forms the # ■ita galli.’ Now not one of these cartilaginous representatives of the parts he compound bone called ‘ethmoid’ in anthropotomy, is united or con- i' ed with the portions of the frontal in mammals which Cuvier has assumed 1 e the homologues of the [irefrontals in the crocodile ; those bones being