304 ZOOLOGY SECT. 



rence as a complete covering is characteristic of the group and 

 almost peculiar to it. When scales are not present, the epidermis is 

 always hardened and cornified so as to form plates of horny material, 

 such as the horny plates of the Tortoises, which protect the under- 

 lying parts from injury and desiccation. Bony plates are frequently 

 present as well. In most respects the internal structure of the 

 Reptilia shows a very decided advance on that of the Amphibia. 

 The skull and the pectoral and pelvic arches are more com- 

 pletely ossified, and both vascular and nervous systems show a 

 higher grade of organisation. 



1. EXAMPLE OF THE CLASS. A LIZARD (Lacerta). 



The most striking external differences between the Lizard (Fig. 

 971) and the Frog are the covering of scales, the comparative 

 smallness of the head, and the presence of a distinct neck, the great 



FIG. 971. Lacerta viridis. (After Brehni.) 



length of the caudal region, the shortness of the limbs, and the 

 approximate equality in length of the anterior and posterior pairs. 

 The anterior limbs are situated just behind the neck, springing 

 from the trunk towards the ventral surface. The fore-limb, like 

 that of the Frog, is divided into three parts, the upper-arm or 

 brachium, the fore-arm or anti-bmnchium, and the hand or manus ; 

 there are five digits provided with horny claws, the firet digit or 

 pollex being the smallest. The hind-limbs arise from the posterior 



