160 FOSSIL BIRDS. 



primum mobile of flight . The opposite crest is not so long, 

 its edge is rounded, and a httle curved behind, where it forms 

 towards the head of the bone a small crook. Under this crook 

 is the hole by which the air penetrated into the cavity of the 

 bone. In quadrupeds this head is always round, the crests 

 small, and that part of them near the head forms tuberosities. 



Even the bats do not resemble birds in the humerus. The 

 mole alone exhibits any analogy with them in this respect, 

 because the manner in which that animal throws the earth 

 backward in burrowing, equally demands a great force in the 

 pectoral muscles. But it is useless to dwell on this exception, 

 as the rest of the humerus of the mole is distinguished by such 

 extraordinary forms, that it is impossible to confound it, not 

 only with the humerus of birds, but with that of any other 

 known animal. 



The character of the lower head of the humerus of birds is 

 not less striking than that of the upper. The articulating 

 pulley is divided into two parts, one internal, or inferior, almost 

 round, for the cubitus ; another external, or superior, for the 

 radius. This last is oblong, in the direction of the length of 

 the bone, and thus re-ascends a little obliquely over its anterior 

 face. In this manner the radius has a greater arch to describe 

 than the cubitus, and the motion of the fore-arm is not made 

 on a plane, perpendicular to the anterior face of the humerus. 



The lower part of this radial face enlarges behind, and rests 

 on an external articulary facet of the cubitus. 



There is nothing similar in the quadrupeds. The cubital 

 pulley is always concave, and the radial is also hollowed in 

 a furrow, in such animals as have not the power of supination in 

 the fore-arm. 



All these distinctive characters of the humerus of birds are 

 found in certain specimens from Montmartre. The characters 

 of the radius are also found in certain speciniens from the same 

 place ; all have the upper head round, and a little concave — 

 the smallest has the inferior extremity more enlarged, precisely 

 as in the birds. 



