IV. Order OPHIDIA. 



Quadrate bone distally free ; temporal region with one 

 temporal arch ; the two parts of the mandible connected by- 

 ligament; teeth not in alveoli. Anal opening transverse; copu- 

 latory organ present, paired. 



Snakes have no movable eyelids, the lid forms a transparent 

 disk over the eye; the ear-opening is absent; the tongue is 

 long and slender, forked, and retractile into a basal sheath. 

 Limbs are absent. 



They may be divided into nine families, seven of which 

 are represented in the Indo-Australian fauna. Poisonous snakes 

 only belong to two of these, Colubridae and Viperidae. 



Synopsis of families. 



A. Eyes under the shields; body covered with uniform 



scaled; mandible toothless Typhlopidae p. 2. 



B. Eyes exposed; median ventral scales usually enlarged; 

 jaws toothed. 



I. Maxillary horizontal. 



a. Traces of hind limbs, ending in a claw, often 

 visible on each side of the anal opening. 



1. Tail prehensile; scales small Boidae p. 14. 



2. Tail not prehensile, very short Ilysiidae p. 34. 



b. No traces of hind limbs. 



1. Mental groove present. 



f A large azygous occipital present ; prae- 



maxillary toothed Xenopeltldae p. 39. 



It No azygous occipital; praemaxillary 



toothless Colubridae p. 41. 



2, No mental groove A»iblycephalidae\).2']T,. 



II. Maxillary short, vertically erectile Viperidae p. 279. 



Indo-australian reptiles II. 



