xiir PHYLUM CHORDATA 325 



suspend the quadrate. The union of the rami of the mandible 

 was ligamentous. There is, as a rule, no sacrum, the ilia not 

 articulating with the spinal column. 



ORDER II. RHYNCHOCEPHALIA. 



Lizard-like, scaly Reptiles with well-developed pentadactyle 

 limbs adapted for walking. The opening of the cloaca is trans- 

 verse. There are no copulatory sacs. The vertebrae are amphi- 

 coelous, sometimes enclosing vestiges of the notochord. The 

 sacrum consists of two vertebrae. Numerous intercentra are present. 

 The ribs have simple vertebral extremities, and are provided with 

 uncinates (see p. 335). There is a system of abdominal ribs. The 

 quadrate is immovably fixed to the other bones of the skull. 

 There are both upper and lower temporal arches. The rami of 

 the mandible are united by ligament. There is a sternum. The 

 teeth are acrodont. The lungs, heart, and brain resemble those 

 of the Squarnata. 



This order comprises only a single living genus, Sphenodon or 

 Hatteria, together with a number of fossil forms. 



ORDER III. CHELONIA. 



Reptilia having the body enclosed in a shell of bony plates, 

 consisting of a dorsal carapace and a ventral plastron, partly of 

 dermal, partly of endoskeletal origin. There is usually on the 

 surface an epidermal exoskeleton of horny plates. The vertebrae 

 and ribs of the thoracic region are firmly fused with the bony 

 carapace, into the composition of which they enter. The quad- 

 rate is immovably united with the skull. The nasal apertures in 

 the skull coalesce into one. The limbs are sometimes terminated 

 by clawed digits adapted for terrestrial locomotion, sometimes 

 modified into the shape of flippers. There are no teeth, and the 

 jaws have a horny investment. The lungs are compound sacs. 

 In essentials the heart and brain resemble those of the Squamata. 

 There are no copulatory sacs, but a median penis. 



This order includes the Land Tortoises, Soft Tortoises, River 

 and Mud Tortoises, and the Turtles, besides a number of fossil 

 forms. 



ORDER IV. THEROMORPHA. 



Extinct Reptiles with amphicoelous vertebrae sometimes enclosing 

 remnants of the notochord, with a sacrum composed of from two 

 to six vertebrae, and with ribs having bifid vertebral extremities. 

 The quadrate is not movable. The limbs are adapted for walking. 

 The pubes and ischia are united. The teeth, which are usually, 

 though not always, present, are highly differentiated and lodged 

 in sockets. 



VOL. II X 



