1845.] OWEN ON SUPPOSED BIRDS' BONES IN THE WEALDEN. 99 



rhomboidal form, as in the Eagle, or is triangular, as in the large 

 Cranes, extending into the anterior concavity, and in all cases nearer 

 to the smaller surface c, than in the fossil. The surface answering 

 to c, also, is always lower down in the humerus of birds; in fact, on 

 the fore-part of the ulnar condyle. The fossil humerus has the ra- 

 dial or outer condyle more produced, more extensive and thinner ; 

 the whole distal end expands more graduallj^ and to a greater ex- 

 tent in the fossil in proportion to the diameter of the shaft, i, e. than 

 in any bird's humerus. If the surface b (fig. 1 & 3) be the anterior 

 extremity of an oblique elliptic articular tuberosity, answering to 

 the radial tuberosity in the bird's humerus, it is nearer the middle 

 of the distal end of the bone, as it is in Bats and Pterodactyles ; and 

 the outer distal surface a is broader than the analogous surface, 

 which rests on the radio-ulnar ligament in Birds. 



The linear ridges c?, like those that afford attachment to the apo- 

 neurotic thecae, which bind down the tendons as they glide along 

 the metatarsus to the toes, in Birds, are not present on the fore-part 

 of the humerus of Birds ; but similar ridges are present on the back 

 part of the upper half of that bone, and they exist in most of the 

 long bones of Pterodactyles. 



In short, the amount of resemblance and of difference respectively, 

 which is demonstrable between the fossil and what I take to be the 

 corresponding bone in Birds, is such as is found in certain bones of 

 those bird-like reptiles the Pterodactyles. 



The distal end of the humerus in the Pterodactylus niacronyx 

 from Lyme Regis, now in the British Museum, described and figured 

 by Dr. Buckland in the ' Geological Transactions,' vol. iii. 2nd series, 

 pi. 27, shows the same general form and gradual expansion ; but the 

 condition of the fossil does not permit the comparison to be pursued 

 into the needful details for Fig. 5. 



unequivocal determination. 

 I proceed, therefore, to give 

 the result of my re-examina- 

 tion of the second of the most 

 characteristic fossils from the 

 Wealden, attributed to a bird, 

 that, viz., which I formerly 

 stated in the note cited by 

 Dr. Mantell to be " very like 

 the head of the humerus of 

 a bird, but to differ from 

 any in the Museum of the 

 College in the sudden ex- 

 pansion of the head*." 



This expansion is due to 

 the outward extension of the 

 broad and thin process g, ' 



fig. 5, answering to the outer 



or deltoidal ororess in fVip '^"'♦'^crior surface of the proximal cud of the hmncius of 



I 



process 



•lor surtace oi lue proxuuai 

 a Pterodaotvlc. Wealden. 



* Loc. cit. p. 17G. 



