410 mr. e. w. hooley on THE [June 19 13, 



The Femur. 



The terminal head and neck, the straightness of the shaft, its 

 attenuation in the median region, and its length, separate the 

 femur of Ornitliodesmus from those of Ornithostoma and Nycto- 

 saurus. In the two last-named the head and neck are placed at 

 a slight angle to the shaft, which is shorter, stouter, and more 

 curved than in the first-named. In the high development of 

 the great trochanter it resembles Ornithostoma. The femur of 

 Bhamphorhynchus differs in the robustness of the neck (which is 

 nearly of the same size as the head), in the divergence of the neck 

 from the shaft, in the comparatively-massive build of the proximal 

 end, and in the shortness of the bone. 



The femur of Pterodactylus resembles that of Bhamphorhynchus: 

 in the thick neck being set at an angle to the shaft, and in the 

 undeveloped condition of the great trochanter ; but it differs from 

 that genus and approaches Ornitliodesmus in the straightness 

 and length of the shaft. The same thickness of the neck and 

 inclination of the shaft are found in Dorygnathus, and apparently 

 in Dimorphodon and Scaphognathus; although in Dimorphodon 

 these characters are not well seen, for the head of the femur is- 

 lying within the acetabulum, and in Scaphognathus it is not well 

 preserved enough to determine with accuracy. The femur of 

 Ornitliodesmus is separated by its terminal neck and head from 

 any known genus of the Ornithosauria, and reveals a higher 

 specialization. 



Y. Conclusions and Classification. 



It is more than probable that, if the type-skulls of Scaphognaikus 

 crassirostris and Dimorphodon were not crushed, they would be 

 found to possess the lizard-like occiput of Ornitliodesmus. 



Although the general outline of the skull reminds one of 

 Pterodactylus, its structure differs quite fundamentally, for it is- 

 essentially similar to the plan of Scaphognathus and Dimorphodon. 

 The separation of the nares from the preorbital fossae is found in 

 each. These skulls were increasing in lightness by the enlarge- 

 ment of the vacuities, andthe reduction of their elements into thin 

 bands and rods. The outcome of this adaptation was the severance 

 of the jugal from the supra-temporal arcade, which in its genesis 

 is seen in Scaphognathus purdoni and in its accomplishment in 

 Ornitliodesmus latidens. The triangular form of the jugal in the 

 former had become an attenuated hollow rod in the latter, producing 

 an incomplete orbit and an infra-orbital vacuity. The separation of 

 the jugal, quadratojugal, and quadrate one from the other had also 

 begun. The shape of the alveoli in Sc. purdoni proves that the 

 teeth were semi-elliptical, thus approximating to the laterally- 

 compressed form of Ornitliodesmus. A vestige of the overlap of 

 the teeth of Sc. crassirostris and Dimorphodon is found in Ornitlio- 

 desmus in the last teeth of the upper jaw. The foregoing facts are 

 strong evidence that the skull of Ornitliodesmus is the highly- 

 modified skull of Scapjhognathus. 



