taught, and that this unity exists in the parts of the same animal has, of late years, been demonstrated. The importance of the vertebræ as segments of the neuroskeleton of the higher animals had been long known, when, in 1806, it occurred to Oken that the bones of the skull, however complicated, were yet but modified vertebræ. Another homology was soon discovered by Spix, who regarded the maxillary arch," the arm of the head," a view which their being both used in prehension of food strengthens. Such doctrines were scoffed at as transcendental;" and, even in 1845, the editor of Cuvier's works, exclaims: "Pour moi une mâchoire supérieure est une mâchoire supérieure et un bras est. un bras. Il ne faut pas chercher à faire sortir, l'osteologie d'un systéme de metaphysique." To which Owen replies: "But a jaw is not the less a jaw because it is a hæmapophysis, nor is an arm the less an arm because it is a diverging appendage." In the same spirit a critic might write "Newton called this earth a planet, and the moon a satellite. For me, the earth is an earth, and the moon is a moon. One must not strive to make an ouranology out of a system of metaphysics." The vertebræ are similar bony segments, jointed in a horizontal line in lower animals, and piled vertically in the skeleton of man. Each is composed of a number of parts, developed in some instances, suppressed in others, but all represented in what is termed the "typical vertebra,' and exhibited in the following figure, with the name opposite to each. The parts enclose a space above termed the "Neural arch," as it lodges the great nervous centre, and another below, which, protecting the great blood-vessels and nutritive organs, is called the "Hæmal" or "Visceral arch." It must be borne in mind that this typical vertebræ is ideal; yet it may be examined, in a very perfect condition, in the skeleton of fish, caudal vertebra of crocodile, and thoracic vertebra of birds; and thus we are led up to the Mammalian form.

These elements can be found, more or less modified, in cranial, cervical, thoracic, lumbar, pelvic, and caudal vertebræ of all skeletons. It is to be regretted that these names are so novel and apparently pedantic, but Dr. Humphry of Cambridge, in his philosophic treatise on the skeleton, has suggested much simpler expressions. A familiar example will illustrate the necessity for the suppression of some elements in certain parts of the human skeleton; thus, if the ribs or pleurapophyses of the lumbar vertebræ were developed, the abdomen would be as indistensible as the thorax.

Space will not allow me to describe what Maclise called "the archetype skeleton," and which has been constructed by Owen as an ideal type for that of all vertebrata. As shown by the next figure, in which the letters correspond to the last, the skull is composed of four cranial vertebræ-occipital, parietal, frontal, and nasal, corresponding to the four great ganglia, in which the brain is developed-viz., epencephalon, mesencephalon, prosencephalon, rhinencephalon, and the organs

of the senses-hearing, taste, sight, and smell. I shall describe the homology of the first of these, as showing "the nature of limbs," a subject admirably reasoned on and proven, especially from the anatomy of fish and lepidosiren, in Owen's great work bearing that title. The centrum is seen in the basilar process, the neural arch in the foramen magnum, the neurapophyses in the portions at each side, and the neural spine in the expanded

part behind. The condyles represent the zygapophyses; the hæmal arch is transferred to the side of chest, where, the student will be surprised to learn, it forms the upper extremity, the scapula being homologous to the pleura

pophyses, its coracoid process to the hæmapophysis, and the arm, a diverging appendage. Maclise regards the scapula and clavicle as belonging to the neighbouring cervical vertebræ.

The following are the elements of the four cranial vertebræ as represented in the foregoing figure :

Maclise considers the facial bones, the hyoid and the thyroid, cricoid and tracheal cartilages, as parts of the hæmal arches of the corresponding cranial and cervical vertebræ, but the far greater number of tracheal rings than vertebræ throws doubt on the hypothesis.

Constancy in number is very remarkable throughout mammalian skeletons, of which the number of cervical vertebræ is a striking instance, there being but seven in the long-necked giraffe, and the same number in the whale, whose head, like that of fishes, seems directly set on the trunk. The three-toed sloth, where there are

nine, and the sea-cow, where there are but six, are the sole exceptions. The same homology to the elements of vertebræ can be demonstrated in every bone of the body; hence the importance of the theory which Holden calls "the grammar of all osteology."

The Human Family is calculated to include about 1,000,000,000 individuals, the average duration of whose life is such that one dies about every second. The science of ethnology investigates the varieties of this vast multitude, and its difficulties will be understood when it is stated that no less than 3,064 distinct languages, and 1,100 religious creeds are now extant among them. Ethnological dynamics considers the influences which, working for centuries, have produced varieties among men. Among those that are physical are climate, soil, and food, besides which mental culture has remarkable influence. Agassiz remarks that all round the arctic circle, and thus, in every longitude there is as striking a similarity between the men as between the fauna and flora of each region. Such are the Laplanders, the Esquimaux, and the Samoiedes, on the European, American, and Asiatic continents respectively. Civilization produces many differences of individual physiognomy, for there is the closest similarity in the countenances of the members of any savage tribe. The effect of food in altering the characters of man has been painfully illustrated in our own country, for no one can have failed to remark how much the sad famine years depressed the physical and mental characters of the western and southern people, or how, under Providence, more prosperous times have again ameliorated their condition in both these respects. Sometimes, however, we cannot perceive the effect of such influences, acting for a short number of years, or in one generation, as the European, American native, and Negro, are found to preserve their distinctive characters under very similar circumstances. So gradual, then, are such changes, that many think it