Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal college of surgeons, in 1843 / by Richard Owen ; from notes taken by William White Cooper ... and revised by Professor Owen.

Date:: 1843

Credit: Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal college of surgeons, in 1843 / by Richard Owen ; from notes taken by William White Cooper ... and revised by Professor Owen. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$forms one great air-cell, -with thin bony parietes; and in this bird, in the Swifts, and the Humming-birds, every.bone of the skeleton, down to the phalanges of the claws, is pneumatic. The extent to which the skeleton is permeated by aii', varies in diflferent birds, in relation chiefly to their different kinds and powers of flight. The opposite extreme to the Swift is met with in the terrestrial Apteryx and aquatic Penguin, in which not any bone of the skeleton receives air. In the mammalian class the air-cells of bone are confined to the head, and are filled from the nasal or tympanic cavities, never from the lungs. The frontal, sphenoidal, and maxillary sinuses, and the mastoid cells, are examples of pneumatic bones in the human subject. The frontal sinuses extend backwards over the calvarium in most Ruminants, and penetrate the cores of the horns in oxen, sheep, and a few antilopes. The whole diploe of the upper, back, and side w^alls of the cranium was inflated, as it were, with air in the great extinct Sloths ; the outer table was raised considerably above the vitreous, and the brain thus seemingly defended by a double skull; the advantage of which modification to these leaf-devouring animals, in the event of blows from the falling trees which they uprooted, is well displayed in the healed fractures of the skull of the Mylodon, in the museum of the College (xii. p. 157.). The outer table of the entire epicranium is similarly raised above the inner one by intervening large air-cells, and their sinuous septa, in the Gii’affe; the short horns are solid, but are sustained by the vaulted roof of the skull; and, as the animal can deal heavy blows with these simple weapons, the concussion is diminished by the interposition of these air-chambers between the outer table and the immediate covering of the brain. The most remarkable development of air-cells in the mammalian class is, however, presented by the Elephant; the intellectual phy- siognomy of this great Pachyderm being caused, as in the Owl, not by actual capacity of the brain-case, but by the enormous extent of the pneumatic cellular diploe between the two tables of the skull. In each of these modifications the vacuities of the osseous tissue, whether mere cancelli as in the Tortoise, or small medullary cavities as in the Crocodile, or larger medullary cavities as in Mammals, or pneumatic cavities and sinuses, are the result of secondary changes by absorption, and not of the primitive constitution of the bones. These are in all air-breathing animals solid at their first commence- ment, and the vacuities are formed by the removal of osseous matter previously formed, whilst fresh bone is added to the exterior surface. n 2$