XII SKELETON — SKIN 497 



girdles. This loss of limbs is as a rule correlated with an 

 elongation of the trunk, not always at the expense of the tail, 

 which in such cases is much shortened. The vestiges of the 

 hind-limbs come to lie as near the vent as possible. This 

 reduction of the limbs occurred in several families which are 

 not directly related to each other. Moreover, it does not occur 

 in all the members of the family, not always in those of the 

 same genus, and there is a considerable amount of individual 

 variation. In most cases of reduction the fore-limbs disappear 

 before, or are smaller than, the hind-limbs. In the Amphis- 

 baenidae (cf. Chirotes, p. 5 66), and in the Tejidae the reverse 

 takes place. In extreme cases the reduction is so complete that 

 even the pectoral girdle has disappeared, leaving scarcely any 

 trace, e.ff. in Bibamus, p. 564. 



The skin is normally covered with scales, which are formed l)y 

 the cutis and liave a horny epidermal coating. The latter, thin 

 and transparent, is shed periodically, peeling off in flakes, ex- 

 cept in Anguis and perhaps other snake-shaped creatures, which 

 shed the skin in one piece. In the Am})hisbaenidae the scales 

 have practically disappeared. When well developed the scales 

 are prominent, and imbricate or overlap with their free posterior 

 edges ; but in many cases the scales are not " scale-like " at all, 

 only like little tubercles, which give the skin a granular 

 appearance. Frequently, for instance in the Scincidae and 

 Anguidae, all the scales contain " osteoderms," or ossified portions 

 of the cutis, and encase the whole body and tail. In other 

 families, e.g. Lacertidae, such osteoderms are restricted to the 

 scales or shields on the head, where they come into contact and 

 fuse with the underlying cranial bones, and moreover roof in the 

 supratemporal fossa. 



The skin of the x4utosauri is entirely devoid of glands. The 

 femoral and pre-anal pores of many families, occmring (^specially 

 in the males, are probably not glands. They are arranged in 

 rows on the under siurface of the thighs and in front of the anal 

 opening. Each of these organs perforates a scale and leads into 

 a tuljular invagination, w^hich is lined with epidermal cells, the 

 proliferation of which produces a horny yellowish debris, and this 

 fills the tube and appears above the surface in the shape of a 

 little cone. The use of this " excretion " is unknown ; it is 

 possibly hedtmic. 



\0L. viii 2 K 



