The corresponding parts in different animals are called homologues, [639] a term first applied to anatomy by the philosophers of Germany; and this term Mr. Owen adopts, to the exclusion of terms more loosely denoting identity or similarity. And the Homology of the various bones of vertebrates having been in a great degree determined by the labors of previous anatomists, Mr. Owen has proposed names for each of the bones: the condition of such names being, that the homologues in all vertebrates shall be called by the same name, and that these names shall be founded upon the terms and phrases in which the great anatomists of the 16th, 17th, and 18th centuries expressed the results of their researches respecting the human skeleton. These names, thus selected, so far as concerned the bones of the Head of Fishes, one of the most difficult cases of this Special Homology, he published in a Table,[44] in which they were compared, in parallel columns, with the names or phrases used for the like purpose by Cuvier, Agassiz, Geoffroy, Hallman, Sœmmering, Meckel, and Wagner. As an example of the considerations by which this selection of names was determined, I may quote what he says with regard to one of these bones of the skull.
[44] Lectures on Vertebrates. 1846, p. 158. And On the Archetype and Homologies of the Vertebrate Skeleton. 1848, p. 172.
“With regard to the ‘squamosal’ (squamosum. Lat. pars squamosa ossis temporis.—Sœmmering), it might be asked why the term ‘temporal’ might not be retained for this bone. I reply, because that term has long been, and is now universally, understood in human anatomy to signify a peculiarly anthropotomical coalesced congeries of bones, which includes the ‘squamosal’ together with the ‘petrosal,’ the ‘tympanic,’ the ‘mastoid,’ and the ‘stylohyal.’ It seems preferable, therefore, to restrict the signification of the term ‘temporal’ to the whole (in Man) of which the ‘squamosal’ is a part. To this part Cuvier has unfortunately applied the term ‘temporal’ in one class, and ‘jugal’ in another; and he has also transferred the term ‘temporal’ to a third equally distinct bone in fishes; while to increase the confusion M. Agassiz has shifted the name to a fourth different bone in the skull of fishes. Whatever, therefore, may be the value assigned to the arguments which will be presently set forth, as to the special homologies of the ‘pars squamosa ossis temporis,’ I have felt compelled to express the conclusion by a definite term, and in the present instance, have selected that which recalls the best accepted anthropomorphical designation of the part; although ‘squamosal’ must be understood and applied in an arbitrary sense; and not as descriptive of a scale-like [640] form; which in reference to the bone so called, is rather its exceptional than normal figure in the vertebrate series.”
The principles which Mr. Owen here adopts in the selection of names for the parts of the skeleton are wise and temperate. They agree with the aphorisms concerning the language of science which I published in the Philosophy of the Inductive Sciences; and Mr. Owen does me the great honor of quoting with approval some of those Aphorisms. I may perhaps take the liberty of remarking that the system of terms which he has constructed, may, according to our principles, be called rather a Terminology than a Nomenclature: that is, they are analogous more nearly to the terms by which botanists describe the parts and organs of plants, than to the names by which they denote genera and species. As we have seen in the History, plants as well as animals are subject to morphological laws; and the names which are given to organs in consequence of those laws are a part of the Terminology of the science. Nor is this distinction between Terminology and Nomenclature without its use; for the rules of prudence and propriety in the selection of words in the two cases are different. The Nomenclature of genera and species may be arbitrary and casual, as is the case to a great extent in Botany and in Zoology, especially of fossil remains; names being given, for instance, simply as marks of honor to individuals. But in a Terminology, such a mode of derivation is not admissible: some significant analogy or idea must be adopted, at least as the origin of the name, though not necessarily true in all its applications, as we have seen in the case of the “squamosal” just quoted. This difference in the rules respecting two classes of scientific words is stated in the Aphorisms xiii. and xiv. concerning the Language of Science.
Such a Terminology of the bones of the skeletons of all vertebrates as Mr. Owen has thus propounded, cannot be otherwise than an immense acquisition to science, and a means of ascending from what we know already to wider truths and new morphological doctrines.
With regard to one of these doctrines, the resolution of the human head into vertebræ, Mr. Owen now regards it as a great truth, and replies to the objections of Cuvier and M. Agassiz, in detail.[45] He gives a Table in which the Bones of the Head are resolved into four vertebræ, which he terms the Occipital, Parietal, Frontal, and Nasal Vertebra, respectively. These four vertebræ agree in general with what Oken called the Ear-vertebra, the Jaw-vertebra, the Eye-vertebra, and [641] the Nose-vertebra, in his work On the Signification of the Bones of the Skull, published in 1807: and in various degrees, with similar views promulgated by Spix (1815), Bojanus (1818), Geoffroy (1824), Carus (1828). And I believe that these views, bold and fanciful as they at first appeared, have now been accepted by most of the principal physiologists of our time.
[45] Archetype and Homologies of the Vertebrate Skeleton. 1848, p. 141.
But another aspect of this generalization has been propounded among physiologists; and has, like the others, been extended, systematized, and provided with a convenient language by Mr. Owen. Since animal skeletons are thus made up of vertebræ and their parts are to be understood as developements of the parts of vertebræ, Geoffroy (1822), Carus (1828), Müller (1834), Cuvier (1836), had employed certain terms while speaking of such developements; Mr. Owen in the Geological Transactions in 1838, while discussing the osteology of certain fossil Saurians, used terms of this kind, which are more systematic than those of his predecessors, and to which he has given currency by the quantity of valuable knowledge and thought which he has embodied in them.
According to his Terminology,[46] a vertebra, in its typical completeness, consists of a central part or centrum; at the back of this, two plates (the neural apophyses) and a third outward projecting piece (the neural spine), which three, with the centrum, form a canal for the spinal marrow; at the front of the centrum two other plates (the hæmal apophyses) and a projecting piece, forming a canal for a vascular trunk. Further lateral elements (pleuro-apophyses) and other projections, are in a certain sense dependent on these principal bones; besides which the vertebra may support diverging appendages. These parts of the vertebra are fixed together, so that a vertebra is by some anatomists described as a single bone; but the parts now mentioned are usually developed from distinct and independent centres, and are therefore called by Mr. Owen “autogenous” elements.
[46] Archetype and Homologies of the Vertebrate Skeleton. 1848, p. 81.