110 



THE EXTINCT BATRACHIA, REPTILIA 



There arc, however, other reasons for believing that the femur was directed forwards, 

 and somewhat upwards from the ilium. One is, that the centre of gravity of an elongate 

 reptilian dorsal and sternal region must have been further forwards than in the short- 

 bodied bird, and therefore the knee must have been further forward, in order to bring the 

 support, i. e., the tibia, etc., beneath it. Another is, that the articulation of the tarso- 

 metatarsal bones with the tibia is excessively oblique, requiring that one or both sections 

 of the limb should be very oblique to the vertical line. As the tarso-metatarsal elements 

 support the weight immediately on the ground, and as it is obvious that the leverage 

 moving the great weight of the body on its support must have been the gastrocnemius 

 and soleus muscles extending the tibia on the metatarsal segment as tin; fixed point ; and 

 as there is no indication of correspondingly powerful muscles to flex the metatarsals on. 

 the phalanges; it is obvious that the latter has been the more vertical, and the former the 

 more oblique segment. And if the tibial segment has been oblique, for reasons just 

 given, the femur must have been oblique also.* 



The length of the femur has had relation to another peculiarity as well, as follows: 



In an animal designed to walk erect, it is necessary that the centre of gravity should 

 be transferred as fir posteriorly as is consistent with the. type. In Laelaps and other l)i- 

 nosauriawe have very elongate pubic and iliac bones, and as I have before described, these 

 appear to have been designed to enclose and support an abdominal mass, in a position 

 beneath the sacrum, and posterior to the position observed in quadrupedal mammals and 

 reptiles. We would thus have a prominent keeled belly between the; femora, supported 

 by elongate curved ischia behind, and slender pubes directed downwards in front. In 

 Poecilopleurum the space between the latter and the sternum was occupied by abdominal 

 ribs. The length of femur places the arc through which the knee moves beyond this pro- 

 jection. 



The confluence of a greater number of vertebra; to form a sacrum seen in this order 

 and in the birds, would seem to have a direct relation to the. support of the above men- 

 tioned greater weight by it, than in horizontal vertebrata, where the weight is distributed 

 throughout the length of the vertebral column. 



The shifting of the neural arches backwards, seen in the same orders, pointed out by 

 Owen, would have a mechanical relation to tin; same necessity; i. <•;., their partial transfer 

 over the intervertebral spaces naturally tending to strengthen the union of the sacral ele- 

 ments. 



The foot need not however have been placed precisely beneath the centre of gravity of 



* Probably in a squatting posture the animal rested on the entire sole as far as the heel, though not under 

 ordinary circumstances ; as I have suggested in Amcr. Naturalist, I., 28, Myeteria and other wading birds assume a 

 similar position at times. 



