250 PALEONTOLOGY 



conglomerate also differ in having some of their ribs articulated 

 by a head and tubercle to two surfaces of the vertebra, as at 

 the anterior part of the chest in crocodiles and Dinosaurs. 

 The shaft of the rib was traversed, as in the Protorosaur and 

 Bhynchosaur, by a deep longitudinal groove. Some fragmen- 

 tary bones indicate obscurely that the pectoral arch deviated 

 from the crocodilian, and approached the lacertian or enalio- 

 saurian type, in the presence of a clavicle, and in the breadth 

 and complicated form of the coracoid. The sacrum includes at 

 least three vertebrae. The humerus appears to have been little 

 more than half the length of the femur, and to have been, like 

 that of the RhyncJiosaurus, unusually expanded at the two 

 extremities. The femur is chiefly remarkable for a third 

 process or trochanter, just above the middle of the shaft, 

 which shows a medullary cavity. The distal condyles are 

 flattened, the outer one being the larger ; there is a deep 

 depression between them posteriorly, and a very light one 

 anteriorly. 



The tibia, fibula, and metatarsal bones manifest, like the 

 femur, the fitness of the Saurians for progression on land. The 

 ungual phalanges are sub-compressed, curved downwards, 

 pointed, and impressed on each side with the usual curved 

 canal. 



The following conclusions may be drawn from the know- 

 ledge at present possessed of the osteology of the Thccodonto- 

 saurus and Palceosaurus : in their thecodont type of dentition, 

 biconcave vertebrae, double-jointed ribs, and proportionate size 

 of the bones of the extremities, they agree with the amphi- 

 ctelian crocodiles ; but they combine a dinosaurian femur, a 

 lacertian form of tooth, and a lacertian structure of the pec- 

 toral and probably pelvic arch with these crocodilian charac- 

 ters ; and they have distinctive modifications, such as the 

 moniliform spinal canal, in which, however, the almost con- 

 temporary Bhynchosaur participates. It would be interesting 



