CHOMDATA. SUMyfART OF UIPORTANT FACTS. 655 



Ichthyopsida, because of their branchife and aquatic habit. They 

 are poikilothermous (cold-blooded). 



33. The reptiles, birds, and mammals are called Amniota on 

 account, of the embryonal organs, the amnion and allantois. They 

 never respire by gills (although gill clefts occur in the embryo), 

 and the appendages are based on the pentadactylc type. 



34. The Eeptilia are poikilothermous, have a strongly ossi- 

 fied skeleton, with unpaired occipital condjde and usually an 

 OS transversum in the skall; a strongly cornified skin, two auricles, 

 and usually two incompletely separated ventricles in the heart. 



35. Recent reptiles are divided among the Chelonia, Rhyncho- 

 cephalia, Squamata (including Lacertilia and Ophidia), and 

 Crocodilia. To these are added the extinct groups Theroniorpha, 

 Plesiosauria, Ichthyosauria, Dinosauria, and Pterodactylia. 



36. The Chelonia are compact, have a skeletal capsule (carapace 

 -|- plastron) composed of bone and horny plates, an immovable 

 quadrate and hard palate, no os transversum or teeth, Ijut horny 

 plates in tlie place of the latter; the cloacal opening elongate, with 

 an unpaired penis in front. 



37. The Squamata have horny scales periodically renewed, a 

 transverse cloacal opening, with behiiid it paired penes and a 

 movable quadrate. 



38. The Lacertilia have usually movable eyelids, tympanic 

 membrane, four appendages or their rudiments, and all but invari- 

 ably a sternum. 



39. The Ophidia lack appendages, sternum, and tympanum; 

 the eyelids are fused to a false cornea; the mouth is usually exten- 

 sible ; poison fangs are frequently present. 



40. The PJiijnclioceplMlia resemble the Lacertilia in form, but 

 differ in having a fixed quadrate. 



41. The Crocodilia are elongate, have bony plates in the skin, 

 elongate cloacal opening, fixed quadrate, teeth placed in separate 

 alveoli, and a long swimming tail. 



42. The Ayes (birds) are closely related to the reptiles (Sau- 

 ropsida) and share with them the single occipital condyle. They 

 are distinguished by the feathers, and by having the heart com- 

 pletely divided into right and left halves. 



43. Other characters are homoiothermy (warm-blooded), pneu- 

 maticity of bones, fusion of bones of manus, formation of tibio- 

 tarsus and tarso-metatarsus (intertarsal joint). 



44. The birds are divided into Ratitc, which lack a furcula and 

 a keel to the sternum, and the Carinatce, in which the sternum is 

 keeled and the clavicles are united to a furcula. To these are 



