ORGANIZATION OP THE OENITHOSAITEIA. 105 



bones in birds. The fibula, slender, style-like, developed cbiefly 

 at the proximal end (PL XI. fig. 8,/), is often prolonged, no 

 thicker than a thread, down the tibia to its distal end. The tibia 

 expands moderately at the proximal end, is elongated, and termi- 

 nates distally in a rounded trochlear end identical with that of 

 birds, and apparently similarly formed by the anchylosed tarsal 

 bone (PL XI. fig. 8, a). This may be seen in DimorpJiodo^i (PL XI. 

 fig. 8) and in many Ornithosaurs from Solenhofen, though the 

 tarsal element is occasionally unanchylosed, as in young birds. 

 This point has some interest, since the blending of the tibia and 

 tarsus is one of the strongest points in Prof. Huxley's definition 

 of a bird. And it seems to assist in modifying Prof. Huxley's 

 assertion that the pes is a part of the skeleton in which birds 

 and Ornithosaurs diverge most widely. 



The metatarsal bones of Ornithosaurs are perhaps the most 

 variable part of the skeleton. They appear to have been applied 

 to the ground as in unguiculate mammals and reptiles, sometimes 

 to have diverged widely, and sometimes to have been packed close 

 together as in Dimorphodon. There is no evidence that they 

 became anchylosed into one mass in any species ; but, on the 

 other hand, the evidence is not perfectly satisfactory that the 

 metatarsal bones were anchylosed in ArclicBopteryx. 



Ornithosaurs have either four or five toes, in which the phalanges 

 appear usually to successively increase in number as in birds and 

 lizards. The claws also are large and compressed from side to 

 side as in lizards and birds. 



Thus in the hind limb there is no structure which can be re- 

 garded as truly reptilian, though the separation of the metatarsal 

 bones, taken together with the number of phalanges in the digits, 

 is a closer resemblance to reptiles than to birds. But the partial 

 separation of the metatarsals in the Penguins seems to indicate 

 that total separation of the bones would not be inconsistent with 

 avian structure. 



From this review of the osteology of this group of animals, it 

 seems to follow : — 



(1) that the reptilian hypothesis of their structure, though not 

 without some interesting indications, especially in the vertebral 

 articulation, is in general so unsupported and so opposed to facts 

 that it must be regarded as no longer tenable. 



(2) That if the pneumatic foramina and cerebral structures had 



