The principal forms of the skeleton and the teeth : as the basis for a system of natural history and comparative anatomy / by Professor Owen.

  • Owen, Richard, Sir, 1804-1892.
Date:
1860
Catalogue details

Licence: Public Domain Mark

Credit: The principal forms of the skeleton and the teeth : as the basis for a system of natural history and comparative anatomy / by Professor Owen. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    PORTIONS OF DERMO- AND NEURO-SKELETONS- armabillo (Dasypus tricinctiis). In the armadillo tlie dermal bones, Fig. 2, o b, are small, polygonal, usually five- or six-sided, smooth on their inner surface, Fi& 2- which rests on the soft subcutaneous layer of cellular tissue, variously sculptured on the outer and exposed side, but with a pattern constant in, and characteristic of, each species. They are united together at their thick margins by rough or sutural surfaces, and resemble a tessellated pave- ment. The trunk is protected by a large buckler of this bony armour; the head is defended by a casque of the same; and the tail is encased in a sheath of similar interlocked ossicles. To allow of the re- quisite movements of the trunk in the small existing armadillos, which, when attacked, roll themselves into a ball, from three to nine transverse rows of the dermal bones, b b, are interposed, having a yielding elastic junction with each other, and with the anterior, o o, and posterior fixed, and larger, parts of the trunk-armour; and by this modification the head and limbs can be withdrawn beneath the armour, when its parts are pulled together by the strong cutaneous muscles into a hemispheric form. In South America, to which continent the armadillos are peculiar, remains of gigantic quadrupeds, similarly defended, have been discovered in the more recent tertiary deposits; but in these colossal armadillos (Glyptodon) the trunk-armour was in one immovable piece, covering the back and sides, and was not divided by bands. Besides the defence which such a modification of the integuments would afford against the attacks of predatory animals, the armadillos and glyptodons habitually frequenting the great forests of South America may have been protected by the same hard, arched covering from falling timber. Such are some of the instances of the structure and uses of the dermoskeleton in the vertebrate province. The development of this system of the skeleton is not dependent on the grade of organization, for we find it in the highest and in the lowest classes; nor does a great amount of osseous matter in the skin necessarily involve a small amount or absence of the same matter in the deeper-seated skeleton; for all the parts of this system of bones, a, c, d, m, ns, are as well developed and as well ossified in the armadillos as in the quadrupeds which are covered by hair. The different states of the neuroskeleton in the sturgeon and armadillo are explicable only with reference to the different media and other conditions under which the two vertebrates were destined to exist. In no species and in no system of the skeleton are bones a primary formation of the animal: they are the result of transmutations of pre-existing tissues, as substances composing animal bodies—e.g., nerve, muscle, membrane, &c.—are called. The inorganic salts, defined in the tabular view of the composition of bone, pre-exist in the blood, in the albumen of the egg of the oviparous vertebrates, and in the milk which nourishes the new-born mammal. The primitive basis, or blastema, of bone is a subtransparent glairy matter, containing a multitude of minute corpuscles. It progressively acquires increased