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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    part of the coracoid by a transversely elongated extremity. It is also expanded at the distal end, where it articulates by cartilage with the ulna and radius. The ulna is a semicircular plate of bone perforated in the centre, and, besides its articulation with the humerus, the radius, and the ulnar carpals and metacarpal ray, it also directly joins the broad coracoid. The radius, after expanding to unite with the humerus, the ulna, and the radial carpals, sends a long and broad process downwards and inwards, which is united by ligament with its fellow and with the lower termination of the coracoid. A basis of adequate extent and firmness is thus insured for the support of the pectoral fins. The carpal bones of these fins are four in number, progressively increasing in length from the ulnar to the radial side of the wrist. The metacarpo-phalangial rays are thirteen in number; the uppermost or ulnar one being the strongest, and articulating directly with the ulna. Proceeding to the next segment, in advance, in the cod-fish's skull, we find that the bone which articulated with the centrum of the occipital segment is continued forward beneath a great proportion of the skull. In quadrupeds, however, the corresponding part of the base of the skull is occupied by two bones ; and if the single long bone in the fish be sawn across at the part where the natural suture exists in the beast, we have then little difficulty in disarticulating and bringing away with it a series of bones similar in number and arrangement to those of the occipital segment. In the skeletons of most animals the centrums of two or more segments become, in certain parts of the body, confluent, or they may be connate ; they form, in fact, one bone, like that, e. g., which human anatomists call sacrum. By the term con- fluent is meant the cohesion or blending together of two bones which were ori- ginally separate; by connate, that the ossification of the common fibrous or cartilaginous bases of two bones proceeds from one point or centre, and so con- verts such bases into one bone : this is the case, e. g., in the radius and ulna of the frog, and in its tibia and fibula. In both instances they are to the eye a single bone; but the mind, transcending the senses, recognises such single bone as being essentially two. In like manner it recognises the occipital bone of man as essentially four bones; but these have become confluent, and were not connate, The centrums of the two middle segments of the fish's skull are connate, and the little violence above recommended is requisite to detach the penultimate segment of the skull. When detached, the bones of it are seen to be so arranged as to form a neural and a hoemal arch. In the neural arch the centrum, neurapophyses, diapophyses, and neural spine are distinct: moreover, the neural spine in the cod, and many other fishes, is bifid, or split at the median line.* The eentrum is called basisphenoid, No. 5; the neurapophysis, alisphenoid, No. 6 ; the neural spine, parietal, No. 7; and the diapophysis, mastoid, No. 8. The alisphenoids protect the sides of the optic lobes, and the rest of the penultimate segment of the brain; the mastoids project outwards and backwards as strong transverse processes, and give attachment to the piers of the great inverted haomal arch. Before noticing the structure of this, I may remark that, in the recent cod-fish, the case, partly gristly, partly bony, which contains the organ of hearing, is wedged in between the last and penultimate neural arches of the skull. The extent to which the ear-case is ossified varies in different fishes, but the bone is always developed in the outer wall of the case. In the cod-fish it is unusually large, and is called petrosal, No. 1G; it forms no part of the segmented neuroskeleton. In the • ArchetypeVert. Skel., p. 11, Fig. 2. J