324 ZOOLOGY SECT. 



OEDER I. SQUAMATA. 



Reptilia in which, the surface is covered with horny scales, 

 sometimes with the addition of dermal ossifications. The opening 

 of the cloaca is transverse in direction. There is a pair of eversible 

 copulatory sacs in the male. The vertebrae are nearly always 

 procoelous. The sacrum, absent in the Ophidia and some Pythono- 

 morpha, consists of two vertebrae in the Lacertilia. The ribs 

 have simple vertebral extremities. The quadrate is usually 

 movably articulated with the skull. There is no inferior temporal 

 arch. The nasal apertures of the skull are separate. The limbs, 

 when present, are sometimes adapted for terrestrial locomotion 

 (Lacertilia), sometimes for swimming (Pythonomorpha). The teeth 

 are acrodont or pleurodont (see p. 345). The lungs are simple sacs. 

 There is always a wide aperture of communication between the 

 right and left divisions of the ventricular cavity. The optic lobes 

 are approximated, and the cerebellum is extremely small. 



Sub-Order a. Lacertilia. 



Squamata in which, as a rule, the limbs are present and are 

 adapted for walking. The mouth is capable of being opened to 

 only a moderate extent. The maxillae, palatines, and pterygoids 

 are incapable of free movement. The rami of the mandible are 

 firmly united at the symphysis. There are nearly always movable 

 eyelids and a tympanum. A sternum and an episternum are 

 present. 



Including all the Lizards, such as the Skincs, Geckos, Monitors, 

 Iguanas, Amphisbsenians, Chamaeleons, and other groups. 



Sub-Order b. Ophidia. 



Squamata with long narrow body, devoid of limbs. The mouth 

 is capable of being opened to form a relatively very wide gape by 

 divarication of the jaws. The maxillae, palatines, and ptery- 

 goids are so articulated as to permit of free movement. The 

 rami of the mandible are connected together only by elastic fibres 

 at the symphysis, so that they are capable of being widely separated. 

 There is no separate supra-temporal ossification. Sternum and 

 episternum are absent. Movable eyelids and tympanum are absent. 



Including all the Snakes Vipers, Rattlesnakes, Sea-Snakes, 

 Fresh-water Snakes, Tree-Snakes, Blind-Snakes, Pythons, and 

 Boas. 



Sub-Order c. Pythonomorpha. 



Extinct Squamata with elongated Snake-like body, provided 

 with limbs which take the form of swimming-paddles. The 

 skull resembles that of the Lacertilia ; a supra-temporal helps to 



