the case of the eye seeing at any time two colours which are in contact, they will appear as dissimilar as possible. In other words, on two colours being seen simultaneously, the complementary of the one will be added to the other. Thus, if a yellowish green leaf and a red flower be under the view at the same time, the yellow green will thereby be more inclined to green, and the red will acquire a slight tinge of blue, and the two will be brought more nearly into the complementary state. In this way the eye itself can rectify any slight defect in the harmonies of adjacent colours.

CHAPTER IV.

THE VERTEBRATE SKELETON.

SECT. I.-THE HOMOLOGIES AND HOMOTYPES OF THE
VERTEBRATE SKELETON.

In the last age there raged a famous scientific controversy, which may be summarily represented as a dispute as to which of the two great principles which we are unfolding should be detected in the animal frame. The illustrious Cuvier, in building up the science of comparative anatomy, proceeded, in all his investigations, on the principle that every particular member of the body had a special or final cause. On the other hand, the great Geoffroy St. Hilaire, first the co-operator and then the rival of Cuvier, delighted to trace a unity of plan running through the bones of the skeleton. In 1830, this controversy came to a public explosion, which was viewed with intense anxiety by all interested in natural science, and in particular by the poet Goethe, who proclaimed it to be a far more important event than the French Revolution, which was ringing that same year in the ears of Europe. In conducting the dispute, extreme positions were taken by both sides. Attached to the principle of final cause, and having found how prolific it was, in his hands, of brilliant discoveries, Cuvier was not willing to admit the theory, (though he helped greatly to establish the fact,) that there is in the skeleton a general corre

spondence of parts, which can have no reference to the wellbeing of the animal, or the special functions of the organ. Geoffroy St. Hilaire, on the other hand, did not see that his doctrine of analogy was perfectly consistent with teleology, and he connected his theory of unity with the untenable doctrine of the transformation of species. This dispute should now be regarded as settled, by the establishment of both doctrines-both that of general homology, and that of special teleology; and the former, we are convinced, will be found, when properly interpreted, to yield as rich a contribution to the cause of natural theology as the latter.

Any one may convince himself, very easily, that in a general sense there are model forms in the construction of the skeleton. He will see at a glance that every species of animal has its normal shape, and this is, to a considerable extent, determined by the length, thickness, and relative position of its bones. In the human frame, there are organs which have been used as standards of measurements, which they could not have been unless their size had been approximately definite. The length of the arm, from the elbow to the top of the mid-finger, furnished the cubit to many nations of antiquity. The hand-breadth and the span were measures among the ancient Hebrews. In not a few countries, the stretch of the arms, the pace, the palm, the breadth of the thumb, have been used to indicate linear measure. Among artists, the human frame has long been known to have proportions in its members. The visible outline of the head in front is divided into four equal parts;-the first, from the top of the head to the setting of the hair; the second, from this to the root of the nose; the third, the nose; and the fourth, from the lower part of the nose to the chin. The height of the figure is found to be eight

heads; the first reaching from summit of head to chin, the second from chin to breast, the third from breast to navel, the fourth from navel to top of thigh, the fifth to middle of thigh, the sixth to knee, the seventh to the calf of the leg, and the last to the heel. The body is thus divided into two equal parts-one from head to hip, the other from hip to heel. The length of the frame is also known to be equal to the line drawn from finger-tops to finger-tops of the outstretched arms.

But without dwelling longer on these general topics, we proceed to shew, in a scientific manner, that the vertebrate skeleton consists of a series of pieces constructed on a common plan; and in doing so, we shall largely avail ourselves of the masterly researches of Professor Owen, who has done so much towards the completion of this most interesting subject.

We know that the skeleton is not a peculiarly interesting object to an untutored eye. It has been associated, in the minds of many, with the grave's mouth and mortality. It possesses in itself no physical beauty; it is meant to be wrapt up from the view by a covering of flesh and muscles, which are made, for our gratification, to present themselves in full and rounded forms. Still, to minds which are fitted to penetrate beneath the surface, it has become an object of intense interest, and is felt to possess not a little beauty. The reason is, that there has been a perception of the unity of the structure along its whole length, and from the highest to the lowest animal in the class, and of the suitableness of the infinitely varied parts to their infinitely diversified functions.

Each of the series of parts which makes up the vertebrate skeleton is called a Vertebra. It will be sufficient for our purpose to indicate here the principal parts of the

M

typical vertebra, without entering into those more minute details which are necessary for the purposes of the comparative anatomist; for these details we would refer to Professor Owen's paper on the Megatherium, in the Philosophical Transactions for 1850.

Typical Vertebra consists of a centre or body, around

d

Ρ

h

H

hs

FIG. 33.*

pl

which are arranged other pieces, (called technically apophyses, or projecting parts,) so as to form two principal arches, one superior, the other inferior. The upper arch gives protection to nervous matter, and is hence called neural: it is bounded on each side by two principal pieces, called neurapophyses, and is closed above by the neural spine, so called from its frequently pointed form; (it is, however,

sometimes bifid.) The lower arch, called hæmal, protects blood-vessels, &c., (hence its name, from Greek, haima, blood;) it also consists of lateral pieces, called respectively pleurapophyses and hæmapophyses, and is closed by the hæmal spine, which, like the neural spine, is sometimes cleft. The body of the vertebra may be considered the foundation of the arches, and the neural and hæmal spines represent, in position, the keystones of each. Sometimes the upper arch comprehends a pair of bones, called diapophyses, and the lower an additional pair, called parapophyses.

1 In the erect position of man, these are respectively posterior and anterior. FIG. 33. Typical Vertebra; ns, neural spine; n, neurapophysis; N, neural arch; e, centrum, or centre piece; pl, pleurapophysis; h, hæmapophysis; hs, hæmal spine: H, hæmal arch; d, diapophysis; p, parapophysis.