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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    concave hind border, and a nearly straight front border; the apex is thick and truncate, with an oval surface divided into two facets. The hind border forms a part of the glenoid cavity ; the front one is a rough epiphysial surface, continuous with a similar but narrower tract, extending upon the anterior border, and by which the scapula articulates with the coracoid. In the iguanians and scincoids this synchondrosis is obliterated, and the two bones are confluent. The hind border of the scapula is nearly straight—the front one sends forwards a process dividing it into two deep marginations. The coracoid in both the varanus and iguana is short and broad; its main body, which articulates with the sternum, is shaped like an axe-blade, and two strong, straight, compressed processes extend forwards from its neck, which is perforated between the origins of these processes and the part forming the glenoid articulations. The clavicles are simple sigmoid styles in the varanus and iguana; are bent upon themselves, like the Australian boomerang, in the cyclodus ; and have the median part of the bend expanded and perforated in lacerta and scincus. They are absent in the chameleon. The sacral vertebrae retain, in some lacertians, the cup-and-ball joints ; and in these—e.g., the scincoids—in which the centrums coalesce, the hind end of the second presents a ball to the first caudal—not a cup, as in the crocodile. In the cyclodus the thick, short, straight pleurapophyses are distinct at their origins from the two coalesced centrums, but coalesce at their ends, that of the first sacral being the thickest. In varanus and iguana the pleurapophyses, as well as the centrums, retain their dis- tinctness, but the hinder ribs incline forwards and touch the expanded ends of the fore pair. These ends are very thick, and are scooped out obliquely behind, so as to present a curved border to the ilium, which Cuvier compares to a horse-shoe. In the varanus and iguana the pleurapophyses of the first caudal incline backwards as much as those of the second sacral do forwards. In the cyclodus they extend outwards, parallel with those of the sacral vertebrse, and are longitudinally grooved beneath. Hsemapophyses are wanting in the first caudal, are developed in the second, and are displaced to the interval between this and the third; they are confluent at their distal end, and produced into a long spine. At the twelfth tail-vertebra the line is obvious that indicates the extent of the anterior detached piece, or epiphysis, of the centrum, immediately in front of the origin of the diapophyses; it continues marking off the anterior third of the centrum in all the other caudals. At this line the tail snaps off, when a lizard escapes by the common ruse of leaving the part of the tail by which it has been seized in the hands of the baffled pursuer. It is a very curious cha- racter, and quite peculiar to the lacertians—this ossification of the centrum from two points and their incomplete coalescence : it adds nothing to the power of bending, or to any other action of the tail, but indicates a prevision of the liability to their being caught by their long tail, and may be interpreted as a provision for their escape. The neural arch has coalesced with the centrum throughout the tail: the epiphysial line does not extend through that arch ; but its thin and brittle walls soon break, when the two parts of the centrum are forcibly separated. Lizards, as is well known, have the power of reproducing the tail, but the vertebral axis is never ossified in the new-formed part. Osteology of Crocodiles.—The numerous and varied forms of fossil bones of extinct reptiles derive most elucidation from the skeleton of the higher organized sauria of Cuvier, which now are rightly held to constitute a distinct order, called Loricata or Grocodilia: a more complete description, therefore, will be given of the skeleton of