U38 



CLASS REPTILIA. 



Fig. 1040. — Part of the left 

 pectoral girdle of Iguana, s, 

 Scapula ; m.sc, Mesoscapula ; 

 cor, Coracoid ; p. cor, Precora- 

 coid ; m.cor, Mesocoracoid ; for, 

 Foramen ; gl, Glenoid cavity. 



frequently united. The vertebras are generally procoelous, although 

 rarely amphicoelous ; their neurocentral suture is always obliterated ; 

 zygosphenal articulations may or may not be present; and inter- 

 centra are always wanting. The dorsal ribs never have uncinate 

 processes ; and true abdominal ribs are 

 likewise never developed. The carpus 

 has but a single centrale ; and the pre- 

 coracoidal process (fig. 1040) is often well 

 marked. 



Three of the groups here regarded as 

 suborders of the Squamata are frequently 

 ranked as distinct orders, but their mutual 

 relations are so close that it appears to 

 harmonise better with the classification, 

 adopted in other branches of the class, to 

 include the whole of them in a single 

 order. The Squamata may be regarded 

 as occupying a position among Reptiles 

 somewhat similar to that held by the 

 Teleostei among Fishes, and the Passeres 

 among Birds. That is to say, they are 

 essentially typical Reptiles, which have 

 attained to a considerable degree of specialisation ; and while they 

 have lost, on the one hand, all signs of kinship with the Amphibians, 

 they exhibit, on the other, no traces of especial relationship with the 

 Birds. That this order has originated from the Rhynchocephalia 

 there seems but little doubt ; but we are very much in the dark as 

 to when or how the divergence took place. 



Suborder i. Lacertilia. — In the true Lizards the four limbs 

 are usually well developed (fig. 1041) but in some cases one or both 

 pairs are wanting. The ali- and orbitosphenoidal regions of the 

 skull are imperfectly ossified ; the superior temporal arcade is 

 generally present ; the quadrate articulates with the pterygoid ; 

 the nasals form a part of the narial aperture ; and the rami of the 

 mandible unite by suture. The vertebrae are in some instances 

 amphicoelous ; they usually have no zygosphenes, and the number 

 in the cervical region does not exceed nine. When limbs are 

 present the pectoral girdle is complete ; and the terminal phalan- 

 geals of the feet are clawed. Dermal scutes are sometimes present ; 

 and these may be developed on the upper surface of the skull, so 

 as to roof over the supratemporal fossae. Existing Lizards are 

 divided into twenty families, but only those will be noticed which 

 occur in the fossil state. 



We may commence our notice with a few Mesozoic forms, of 

 which the family position is not yet determined. The earliest 



