AMPHIBIANS AND REPTILES. 143 
mostly provided with a leathery skin. ‘The skeleton is usually 
firm, and the nervous system is better developed than in the 
fishes and amphibians. ‘The extinct forms are numerous, and 
show close relation with the earlier birds. 
Key to the orders. 
a. Body covered with imbficated scales; dorsal vertebree and ribs movable; 
bones of skull separate; jaws with teeth; vent a cross-slit. 
b. Mouth very dilatable; bones of mandible, and of head generally, united 
by ligaments; limbs wanting, or represented by short spurs on sides 
of vent; no shoulder-girdle; no eyelids; no tympanum. OPHIDIA 
bb. Mouth not dilatable; bones of mandible united by a bony suture in 
front; limbs 4, rarely wanting; shoulder-girdle present; eyelids usually 
present; tympanum usually present. LACERTILIA 
aa. Body short, depressed, enclosed between 2 bony or cartilaginous shields, 
or carapace and plastron, from which the head, limbs and tail may be 
protruded; jaws with a horny shield and no teeth; vent roundish or 
longitudinal, plaited. TESTUDINATA 
Order OPHIDIA. 
The Serpents. 
Body elongate, terete. Mouth very dilatable, bones of both 
jaws and of the palato-pterygoid arch freely movable, united by 
ligaments only. Quadrate bone articulated to the skull. Brain- 
capsule entirely osseous. ‘Tongue forked, capable of protrusion. 
No eyelids. No external ears. Limbs wanting. + Shoulder- 
girdle wanting. Pelvic arch usually wanting, rarely rudimentary, 
and with hinder limbs represented by small spurs on the sides 
of vent. Vent a transverse slit. Copulatory organs present, 
paired. Body covered with imbricated scales which are shed as 
a whole and replaced at regular intervals. 
The snakes may easily be distinguished from most of our other 
vertebrates within the limits of the state, by the absence of limbs. 
Key to the families. 
a. Non-venomous; maxillary horizontal, not excavated; no deep pit between 
eye and nostril; upper jaw with solid teeth only, no grooved perforated 
fangs. COLUBRIDA 
