100 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 17, 



humerus of the bird, and to 

 a corresponding production, 

 though to a less extent, of 

 the opposite or thicker angle 

 fy answering to the inner tu- 

 berosity in Birds. The ex- 

 posed surface of the fossil is 

 therefore the posterior or an- 

 conai surface, towards which 

 the transversely extended ar- 

 ticular head of the bone e is upper view of proximal end of the humerus of a Ptero- 

 inclined. The difference be- dactyle. Wealden. (Natural size.) 



tween the fossil proximal portion of the humerus and that part of the 

 skeleton in birds of flight, is manifested by the more reniform figure 

 of the head e in the fossil (figs. 5 and 6), its closer proximity to the 

 inner tuberosity/, the minor production of that tuberosity, the absence 

 of the cavity on its back part, and of the pneumatic foramen, which 

 in birds of flight is there situated ; and lastly, the greater length and 

 less extent in the direction of the axis of the bone, of the outer plate 

 or process g. 



It may therefore be in- 

 ferred, that the large cavity 

 shown at the broken ends of 

 the fossil (fig. 7) was filled, 

 as in Bats and Pterodactyles, 

 by a light fluid marrow, and 

 not by air. 



The humerus of the Ptero- 

 dactylus macronyx above ci- 

 ted shows asimilar form of the 

 outer proximal plate mark- 

 ed l"*,and though this pro- Lower view ofproximal end ofthe humerus of a Ptero- 

 CeSS is unluckily broken off dactyle. Wealden. (Natural size.) 



in both humeri of that unique specimen, yet its great length is indi- 

 cated by an impression in the matrix. The whole extent of this pro- 

 cess is fortunately shown in the Pterodactylus crassirostris figured 

 by Goldfussf ; and in that of the P. longirostris, given by Cuvier 

 in the 5th volume of the ' Ossemens Fossiles,' pt. ii. pi. 23, Cuvier 

 says, in reference to the humerus of the Pterodactyle, " On peut 

 remarquer que sa tuberosite anterieure, (1) est fort saillante comme 

 dans les tortues de nier et dans les oiseaux, ce qui convenoit tres- 

 bien au premier os d'une veritable aile." (p. 369.) 



The comparison is obviously general, in reference to the modifi- 

 cation of the humerus in relation to flight; but the special difference 

 of form and proportion between the process alluded to in the Ptero- 

 dactyle and the homologous one in the bird, is precisely that which 

 the fossil head of the humerus from the Wealden presents in com- 

 parison with the humerus of a bird of flight. 



* Loc. ante cif. pi. 27. 



t Beitrage zur Kenntniss verschiedener Reptilien r!er Vorwelt ; Goldfuss, Nova 

 Acta, &c., XV. pt. i. p. 63. tab. 7, 8, 9. 



