XI 1 SKELETON 495 



knob. The caudal vertebrae of the Geckones and of most 

 Lacertae are liable to break across, like those of Sphe7wdoii. 

 They are enabled to do this owing to a transverse split, which 

 makes its appearance with the ossification of the vertebral 

 bodies and extends later into and across the neural arch and 

 the various lateral processes. The split is ultimately referable 

 to a transverse septum of cartilage, wrongly called chordal 

 cartilage, wliich develops in the shell of the body of the vertebra, 

 destroys the chorda, and extends peripherally. The cells of this 

 septum retain throughout life their juvenile quasi-embryonic 

 character. When the tail is broken off — and this always happens 

 at such a septum— the cells of the remaining lialf reproduce a 

 new tail. The latter is, however, in reality a sham tail, since 

 neither new centra nor arches, but only a non-segmented rod or 

 tube of fibro-cartilage is produced by this process of regeneration, 

 lieproduction of centra is precluded by the previous normal 

 reduction of the chorda, around which alone proper bony centra 

 could be formed. The regenerated tail is, however, invested 

 with new muscles, and with skin, but the scales often differ 

 considerably from those of the normal organ. Boulenger ^ has 

 found that the new or aberrant scaling is in some cases a 

 reversion to an ancestral form. This is, for instance, the case in 

 Pseudopus, and in the Tejoid genus Gymno^jhthalmus ; to a 

 certain extent also in Geckos and Skinks. On the other hand, 

 Lacertidae, Gerrhosauridae, and also Anguidae reproduce a 

 caudal scaling true to their type. Injured or broken-off tails 

 are often reproduced double, or even trifid ; sometimes an 

 additional little tail grows out from an injured spot, anywhere 

 on the side of the old remaining but mended tail. 



The ribs of the trunk articulate by their capitula only, 

 while the reduced tubercula are attached to their vertebrae by 

 ligaments. In the tail the capitular portion is much reduced, 

 while the tuberculum is much stronger and lies behind, no 

 longer above, the capitulum, fusing sometimes directly with the 

 centrum. The ribs of the poststernal region of Geckos and 

 Chameleons are very long, and meet each other in the middle 

 line, forming thin cartilaginous hoops. 



The limbs are of the typical pentadactyloid type. The distal 

 tarsalia are often fused with the metatarsals, so that the chief 



' P.Z.S. 1888, p. 351, and 1891, p. 466. 



