VERTEBRATA. 21 



protect the brain during the exposure of these animals to the 

 trampling of quadrupeds, &c, whilst concealed in their natural 

 haunts. Their teeth are small, conical, and sharp ; they are placed 

 in the two maxillary, the intermaxillary, and the palate bones. 



Sauria. — In this order we meet with a more perfect development 

 of skeleton than in the last, as they possess a sternum, a scapular 

 and pelvic apparatus, together with atlantal and sacral extremities. 

 The lacerta iguana presents 5 cervical, 11 dorsal, 9 lumbar, 2 

 sacral, and 72 caudal vertebrae ; the crocodile of the Nile 7 cervical, 

 12 dorsal, 5 lumbar, 2 sacral, and 34 caudal — articulated by ball 

 and socket. There are false ribs behind and before the true ones. 

 In the chameleon there are 17 pairs ; in the crocodile 12. The 

 sternum is prolonged posteriorly as far as the pubis, and has attached 

 to it five pairs of cartilaginous arches, for the purpose of supporting 

 the abdomen. 



The head is extended forwards in a line with the spine, as in the 

 other inferior vertebrata ; like these, also, its component elements 

 are loosely connected. As in serpents, the basilar condyle is elon- 

 gated transversely, and the parietal bones anchylosed. The lower 

 jaw consists of six pieces on each side ; and here, as in serpents, 

 the prehensile teeth are attached by broad base to the surface of the 

 jaw, and the new teeth rise by the side of the old, and not in their 

 interior as in the crocodile. 



Anterior extremity. — The scapula is broad, thin, and curved. 

 The acromion is a distinct bone, and the clavicles are anchylosed 

 in form of a cross, on the front of the sternum. The humerus is 

 expanded at its extremities, and the same form as in man ; the ulna 

 is without an olecranon, stronger than the radius, and separated from 

 it below. There are from four to nine bones in the carpus, five 

 in the metacarpus; and the phalanges are, two for the thumb, 

 three for the second and last fingers, and four for each of the 

 others. 



Posterior extremity. — The three portions of the os innominatum 

 contribute to the formation of the cotyloid cavity. The ossa pubis 

 and ischii form a lengthened symphisis in front; and the spine of 

 the iliac bones is extended backwards along each side of the sacrum. 

 From the front of the pubic bone a process passes up towards the 

 sternum as in the marsupiales. The head of the femur is com- 

 pressed and directed forwards ; the great trochanter is also flat and 

 turned towards the tibia. The patella is small ; the tibia short, 

 thick, and curved ; the fibula slender in the centre, expanded at its 

 extremities, and apart from the tibia. In the crocodile there are five 

 bones in the tarsus, four in the metatarsus, and the toes are so 

 arranged that the most internal sustains two phalanges, the second 

 three, and the third and fourth, four each. 



In the skeletons of the nilotic crocodiles, alligators, and other 

 reptiles destined to swim by the lateral movements of a muscular 

 tail and long webbed feet, their long bones are filled with a thin 

 oily marrow, and the bones of the head firmly united. 



