5th. That the whole or archetypal form of which these unequal skeletal figures are the parts, is the only absolutely uniform skeletal series.
6th. That nomenclature and all modes of classification, according to specific distinct nesses, have no real meaning apart from the consideration of this law of an archetypal uniform prime model undergoing a graduated metamorphosis of its parts. That in this higher law of graduated series is enveloped all lesser laws of classes, orders, genera, species, and individuals, which, whatever be the amount of their distinctive characters, do one and all point to a unity of type more or less.
With this purpose before the reader's mind, I proceed to lay down my propositions as preliminaries by which to pioneer a passage through the blinding thicket of nomencla ture and gain the light beyond it, the light of a general law t in nature. But before he passes with me to my task of comparison, I warn him that he should feel within himself a full conviction of the truth, that in order to gain a fair insight of the law of formation, he must not suffer names of different significa tions to hide the common analogy or siinilitude which the things themselves manifest. He must have fully freed himself of the barbarisms of the nomenclature which the unreasoning human anatomist still makes use of ; he must not suppose that because one spinal piece is named sacrum, it is therefore absolutely dif ferent to another spinal piece named vertebra. And even in respect to the name vertebra*, which applies alike to all spinal segments, however quantitatively different these may be, he should not think these the same things in form and dimensions, and elemental consti tuents, simply because they bear the same name.
For in reality this name vertebra attaches to bodies which are quantitatively different, and is, therefore, a name as truly misapplied to generalise notonly over the spinal units of the skeletal axes of the four classes of vertebrata, but even over those of the human type ; as if, while viewing a series of circles, semi circles, and segments, we called it a series of segments of semicircles or of circles, which it evidently is not. We would not call the two
quantities, viz. circle and segment, by the same name ; neither should we name such different quantities as cervical, dorsal, and coccygeal forms under the comtnon title " vertebrm." If we fully ackowledge to this first truth, truth will be begotten of it ; but if we still begin the calculation with the error, error will spring from out of it, and defy all mathematical computation.
Verlebne are unequal quan tities.—In the human spinal axis I find that those bodies which the human anatomist terms vertebrm are not quantitatively similar, equal, or homologous.t The cervical vertebra (A,fig.
4 11.) differs in this respect from the dorsal tenra (c); this from the lumbar vertebra (E); this from the sacral vertebra (u); and this from the coccygeal vertebra (1). In all ani mal spinal axes I seethat those bodies which the comparative anatomist names vertebrm are likewise quantitatively different. The several classes of vertebrx termed cervical, dorsal, lumbar, sacral, and caudal, are actually deve loped of unequal quantities. And it is, more over, tnost true that even the vertebrce of any one class, whether of the cervical class, the dorsal, lumbar, sacral, or caudal, are not quantitatively similar or equal. In animal cer vices, thoraces, or loins, the vertebrm consti tuting any of those regional divisions of the spinal axis are not equal quantities. Even in the human cervix, thorax, or loins, or sacrum, or caudex, the vertebrm of each region mani fest those quantitative differences. For we find in the human neck that B, or in the loins F, occasionally develops a surplus rib (fig.444. B and F, 4); which circumstance gives rise to a serious objection to the rule, that " the mammal cervix is constant to the num ber of seven vertehrm," or that the thorax of even the human skeleton develops twelve vertebrm constantly, or that the human lum bar region is confined to the number of five vertebrm constantly. It is evident, therefore, that the bodies named vertebrm are quantita tively different bodies, as seen not only in all spinal axes comparatively estimated, but even in the one animal spine of human type.