LACERTILIA. 337 



The latter may in some forms (Scincidae, Anguidae, on the 

 head only in Lacertidae) develop bony plates (osteoderms), 

 which on the head may coalesce with the subjacent bones. The 

 scales on the head are arranged much as in snakes and the same 

 nomenclature is used in describing them. The scales may have 

 the form of chagrin-like granules or of variously formed tubercles. 

 In the Amphisbaenidae the skin is soft and scaleless. The 

 horny layer of the epidermis periodically peels oil in flakes, or 

 as in Anguis etc. in one piece. Cutaneous lobes on the throat 

 and sides of the trunk, and crests on the back and top of the head 

 are often present. Cutaneous glands are present on the inner 

 sides of the thighs (femoral glands, Fig. 191a, SP) and in front 

 of the anus, otherwise they appear to be absent. They are 

 tubular structures filled either with a slimy mass or with a short 

 wart-like body of a horny consistency which in the breeding 

 season may project on the surface. They are present in both 

 sexes or only in the males, and are absent in some genera. 



Most lizards are capable of changing colour. This is 

 especially seen in the chameleons. 



The vertebrae are procoelous except in the Geckonidae in 

 which they are aniphicoelous. In this family the notochord 

 persists, except in the middle of the vertebrae, throughout the 

 vertebral column. All the vertebrae in front of that carrying 

 the first sternal rib are cervical. There are one or two lumbar, 

 two sacral, and a large number of caudal. The atlas consists 

 of three pieces, one ventral and two dorso-lateral. The odontoid 

 is closely attached to the axis. The two sacral vertebrae are not 

 ankylosed, but they are united by strong ligaments. The anterior 

 caudal vertebrae have chevron bones attached to the centra and 

 not to the intervals between ; and subvertebral wedge-bones, 

 consisting of small separate ossifications found on the ventral 

 surface at the junction of two vertebrae, are often present on 

 Other parts of the vertebral column. 



Til the Iguanidae the vertebrae are articulated by zygantra and zygo- 

 sphenes as in snakes, in addition to the ordinary articulating processes. 

 In many lizards the caudal vertebrae are composed of two halves, an 

 anterior shorter to which the transverse process is attached, and a longer 

 posterior portion. This phenomenon is due to the presence of a thin 

 unossined transverse septum traversing the vertebrae. As is well known, 

 many lizards when seized by the tail have a habit, of breaking off the part 

 seized and so escaping. Such breaks always take place at one of the weak 

 z. ii. z 



