484 REPTILES. 



to do with ribs, but are ossifications in the fibrous tissue which lies 

 under the skin and above the muscles. They form seven transverse 

 series, each composed of several ossicles. 



As to the skull, there is an interorbital septum with large alisphenoids ; 

 the presphenoid and orbitosphenoids are at best incompletely ossified ; 

 all the bones are firmly united by persistent sutures ; both upper and 

 lower temporal arcades are completely ossified ; the maxillse, the pala- 

 tines, and the pterygoids meet in the middle line of the roof of the 

 mouth, covering the vomers, and determining the position of the pos- 

 terior nares — at the very back of the mouth ; an epi-pterygoid connects 

 parietal and pterygoid ; an os transversum extends between the maxilla 

 and the junction of palatine and pterygoid ; the quadrate is large and 

 immovable ; there are large parotic processes ; the tympanic cavity is 

 completely bounded by bone ; the teeth, which are borne by premaxillse, 

 maxillae, and dentaries, are lodged in distinct cavities ; beside and even- 

 tually beneath the teeth lie reserve " germs " of others. 



Each ramus of the mandible consists, as in most Reptiles, of a cartilage- 

 bone — the articular — working on the quadrate, and five membrane-bones 

 — dentary, splenial, coronoid, angular, and surangular. 



The hyoid region is very simple. 



In the pectoral arch there are no clavicles nor epicoracoids, but 

 there is a so-called interclavicle or epistemum ; the fore-limb is well 

 though not strongly developed ; there are five digits, webbed and 

 clawed. 



In the pelvic arch, large ilia are united to the strong ribs of the two 

 sacral vertebrae ; the pubes slope forward and inward and have a cartila- 

 ginous symphysis ; the ischia slope backward and have a symphysis ; 

 ilia and ischia form almost the whole of the acetabulum. The hind- 

 limbs bear four digits, webbed and clawed. 



Some of the Characteristics of the various organs of 

 Crocodilians. 



The Crocodilians are seen to best advantage in the water, swimming 

 by powerful tail-strokes. The limbs are too weak for very effective 

 locomotion on land, the body drags on the ground, and the animals are 

 stiff-necked. Although many, especially in their youth, feed on fishes 

 and small animals, the laiger forms lurk by the edge of the water, lying 

 in wait for mammals of considerable size. These they grasp in their 

 extremely powerful jaws, and drown by holding them imder water. If 

 the dead booty cannot be readily torn, it is often buried and left until it 

 begins to rot. In connection with their way of feeding, we should notice 

 several peculiarities of structure ; as the nostrils are at the upper end of 

 the snout, and the eyes and ears also near the upper surface, the Croco- 

 dilians can breathe, see, and hear, while the body is altogether immersed 

 except the upper surface of the head ; as the nostrils can be closed by 

 valves, and the eyes by transparent third eyehds, and the ears by movable 

 flaps, the head can be comfortably immersed ; a flat tongue is fixed to 

 the floor of the mouth, and the cavity of the mouth is bounded behind 



