470 



REPTILES. 



Again we shall virtually quote from Huxley in noting 

 some of the distinctions between Reptiles and Birds : — 



The exoskeleton consists of horny epi- 

 dermal scales^ or of bony dermal scutes^ 

 or of both. 



The centra of the vertebrse are rarely 

 like those of birds. 



When there is a sacrum, its vertebrae 

 (usually two in number) have large ex- 

 panded ribs, with the ends of which the 

 ilia articulate. 



The cartilaginous sternum may become 

 bony, but is not replaced by membrane- 

 bones, unless perhaps in Pterodactyls. 



When there is an mterclavicle, it remains 

 distinct from the clavicles and sternum. 



The hand has more than three digits, 

 and at least the three radials are clawed. 



In living reptiles the ilia are prolonged 

 farther behind than in front of the aceta- 

 bulum ; the pubes slope downward and 

 forward ; there are pubic and ischiac 

 symphyses. 



There are often five toes ; the tarsals and 

 the metatarsals remain distinct. 



At least two aortic arches persist ; only 

 the Crocodilia have a structurally four- 

 chambered heart ; more or less mixed 

 blood always goes to the posterior body. 



The blood is cold. 



The optic lobes lie on the upper surface 

 of the brain. 



There is an outer covering of feathers, 

 and though there may be a few scales 

 there are never scutes. 



The centra of the vertebrse have usually 

 a peculiar terminal curvature. 



The two sacral vertebrae have no ex- 

 panded ribs, they fuse with others to form 

 a long composite sacrum. 



The cartilaginous sternum ls replaced 

 by membrane-bones from several centres. 



Whenthere is an interclavicle, it is con- 

 fluent with the clavicles. 



The hand has not more than three 

 di^ts, and at most two radials are clawed. 

 The fore-limbs are modified as wings ; 

 some carpals fuse with the metacarpals. 



The ilia are greatly prolonged in front 

 of the acetabulum, the inner wall of which 

 is membranous. The pubes slope back- 

 wards, parallel with the ischia ; only in 

 Struthio^ is there a pubic symphysis, only 

 in Rhea is there an ischiac one. 



There are not more than four toes ; the 

 proximal tarsals unite with the tibia, 

 forming a tibio-tarsus ; the first meta- 

 tarsal if present is free, but the three othera 

 are fused to one another and to the distal 

 tarsals, forming a tarso-metatarsus. 

 _ There is but one aortic arch, to the 

 right ; the heart is four-chambered ; the 

 blood sent to the body is purely arterial. 



The blood is hot. 



The optic lobes lie on the sides of the 

 brain. 



The lungs have associated air-sacs. 



The sutures between the bones of the 

 skull are usually obliterated at an early 

 stage. 



The right ovary atrophies. 



There are five orders of living Reptiles, namely, Chelonia 

 (tortoises and turtles) ; Rhynchocephalia, of which the New 

 Zealand " lizard " Batteria is the only surviving representa- 

 tive ; Lacertilia (lizards), Ophidia (snakes), and Crocodilia 

 (crocodiles, alligators, and gavials). 



But the number of orders is greatly increased when we 

 take account of those extinct Reptiles, which are not refer- 



