FOSSIL BIRDS. 157 



before as accompanying an impression of the body of a bird. 

 That it could not liavc belonged to that body, is proved by 

 the latter having its femora, while there is another femur with 

 the foot, which is moreover much too large in proportion. 

 The foot itself is also too large, and the bones too thick, to 

 suffer it to be confounded with any of the preceding. The 

 characteristics of the bird are all perfect in it. 



From the discovery of some other feet, into a detailed de_ 

 scription of which it is quite unnecessary to enter, the Baron 

 concludes from these alone, that there were at least nine species 

 incrusted in the gypsum . From such a number of fragments 

 attesting, by their assemblage, the existence of ornitholites in 

 the regular rocky strata, it was impossible that any doubt could 

 remain on this subject; and, consequently, the negative argu- 

 ments of Fortis, and other naturalists, against their existence, 

 must fall to the ground before the evidence of facts. 



Several other little isolated bones proved, on examination, 

 to be referrible to the class of birds. A portion of tarsus, 

 divided below into three apophyses, each terminated by a demi- 

 pulley, for the articulation of the first phalanges of the three 

 front toes, proved to be of this description. 



Among the quadrupeds, none but the jerboa and alactaga 

 exhibit any thing similar. But as there is no other indication 

 in all the plaster- quarries of such animals, the remains in ques- 

 tion must not be referred to them. 



The femora of birds have also a distinctive character, which 

 belongs to the peculiar nature of the knee. This articulation 

 in birds is provided with a sort of spring, analogous to the 

 hinges of a clasp-knife. The blade, we know, has but two 

 points on which it can rest steadily ; namely, when it is com- 

 pletely open or completely shut, because there are only those 

 two points on which the spring is not removed from its natural 

 position. 



Now, the birds having but two feet on which to find a solid 

 seat, have received an articulation of this kind with two fixed 



