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  Section: Anatomy of Vertebrate Animals » The Classification and the Osteology of the Reptilia
 
 
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The Chamaeleonida

 
     
 

The Chamaeleons are distinguished from the Kionocrania not only by the negative character of the absence of the columella, which they share with the preceding group, but by a number of very important positive features. Among these I may mention the soft and tuberculated skin, with its changing hues; the absence of any tympanum; the prehensile tail; and the very peculiarly modified feet. The digits are arranged in bundles of two and three, the manus having the pollex, the index, and the medius, syndactylous and turned inward; while, in the foot, it is the hallux and index only which are thus united and turned inward, the three other toes being similarly connected together by integument as far as the ungual phalanges, and directed outward. To these characters may be added the remarkable tongue, capable of protrusion and retraction with almost lightning rapidity.

The vertebrae of the Chamaeleons are similar in their characters to those of the procoelous Kionocrania. The sacrum is composed of only two vertebrae. Only a few of the anterior ribs are united with the sternum. A large number of the posterior ribs, as we have already seen to be the case in the Gecko, unite together in the mid-line, and form continuous hoops across the ventral wall of the abdomen.

But it is in the structure of the cranium that the Chamaeleonida depart most completely from the ordinary Lacertilian type. The parietal bone is not movable upon the occipital, the supra-occipital sending up a median ridge, which unites with the base of a corresponding crest or process extending backward for a considerable distance from the middle line of the parietal bone. The summit of this sagittal crest is joined by two curved prolongations of the squamosal, the three giving the occipital region of the Chamaeleon its remarkable casque-like form.
The frontal bone is comparatively small and single, and the nasals are very narrow, and do not bound any part of the anterior nasal apertures. These apertures, in fact, are situated upon the sides of the fore-part of the skull, and are separated from the nasal bones, in part, by a membrane which stretches outward from the nasal bones; and external to this by a prolongation forward of the prefrontal bone, which unites with the maxilla, and in some specimens of Chamaeleons is prolonged forward into a great osseous horn, projecting from the sides of the front part of the snout.

The orbit is closed behind by the ascending process of the jugal bone, but there is no quadrato-jugal. The quadrate bone itself is not, as in most other Lacertilia, movable upon the sides of the skull, but is firmly anchylosed with the bones which lie adjacent to its upper end. The pterygoid bones are produced downward; and, by a very exceptional peculiarity, do not articulate with the quadrate bones, but are connected with them only by fibrous tissue. In the lower jaw, the dentary piece takes up a very much larger proportion of the ramus than is the case in other Lacertilia The basal portion of the hyoid is represented by a long median cylindrical entoglossal bone, and its posterior cornua are much stronger and longer than the anterior pair. In the pectoral arch the scapula and coracoid are remarkably longer and narrower than in other Lacertilia. There are no clavicles, and the interclavicle is wanting, the sternum being represented only by its rhomboidal ossified cartilage. Again, in the pelvic arch, the ilium is long and narrow, and its long axis is directed nearly vertically to that of the trunk - in which respect the Chamaeleons differ very much from the ordinary Lacertilia. There is no os cloacae.

The carpus and the tarsus have a very singular structure. In the carpus there are two proximal bones, articulated with the radius and the ulna respectively. A single spheroidal bone is articulated with these, and with the five proximal constituents of the digits. Besides these, there is an ossicle representing the pisiform. In the tarsus there are also four bones, two articulated with the tibia and fibula respectively, a third below and between them, and a fourth distal bone articulating with the five proximal bones of the digits. In both manus and pes the number of the phalanges, counting from the preaxial to the postaxial side, is 2, 3, 4, 4, 3.


 
     
 
 
     



     
 
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