THE ANATOMY OF THE LIZAEDS 15 



iarities of the slow-worm to be mentioned separately. 

 More minute details of structure would be beyond the 

 province of this work, and the student is referred for 

 these to the text-books of zoology. 



Skeleton. — The exo-skeleton, or body-covering, con- 

 sists of scales which overlap each other. (The specific 

 arrangement of head scales will be dealt with later.) 

 The scales are derived from the epidermis. They vary 

 in size, character, and arrangement in different parts 

 of the body : those on the dorsal aspect of the body 

 being small and hexagonal and slightly keeled ; those 

 on the ventral or belly surface are much larger and 

 arranged in longitudinal series ; whilst those on the 

 tail are of the same nature all round the circumfer- 

 ence, and are longer than broad, keeled and arranged 

 in transverse series. This causes the annul ated appear- 

 ance of the tail. 



Where the neck joins the trunk there is a fold 

 of skin, in front of which the neck scales are larger 

 than those more anterior still. The head scales are 

 large. The anterior margin of the anal orifice or 

 cloacal opening is formed by a large scale or plate, 

 the pre-anal plate. A little careful study of these 

 points in a lizard will enable the field naturalist 

 to determine the part of the body to which a 

 portion of a slough belongs, and if that slough 

 is from the body or head the species may also be 

 known. 



The endo-skeleton, or bony-skeleton, may be pre- 



