dhe Re aT tere Oe ey Te ee ee eg oes kee eg Ebi = 
a 7 3 fee Sanat 3 
MECHANISM OF FLEXION AND EXTENSION IN BIRDS’ WINGS. 513 
and especially that the two cotyledons originated as it were from the 
y 
one, and he would leave to him the undertaking of reconstructing mor- 
piinlony and phyllotaxis upon such a basis. 
Dr. de OF cE LGARD remarked, that the whole question came back to the 
laws of phyllotaxy. The very fact of these ‘ genetic” numbers, as he 
had called ii ooieoe Á second element to be derived from the first 
one; as all radial organs t be derived from their predecessors. The 
fact itself was raa in re far too much neglected phenomena of cryp- 
togamous developments (or ‘‘ embryology” of authors). “he moss-spore 
l 
of its thread-like “ prothallium.” Each of its cells is generated out of a 
preceding one. A terminal cell enlarges into a conical leaf. Out of that 
leaf springs the second, at its base. It is in fact only on the supposition 
re — alte ng from either border n the case of th - 
leaves, producing fertile ovules), that the whole o ph 
nomena, of organic numbers in general, becomes explicable. The 
uc 
condition. , Cotyledons already formed do not divide. Lobes of fissures, 
folds, etc., of cotyledons are no divisions, but are due to unequal enlarge- 
ent. New elements are not formed by division, but by sprouting. 
MECHANISM OF FLEXION AND EXTENSION IN Birps’ Wixes.— By 
Dr. ELLIOTT Covers. 
Dr. Coves’ proposition is, that flexion of the forearm upon the 
humerus produces flexion (adduction) of the hand upon the 
forearm, by osseous mechanism alone, and conversely: exten- 
sion of the forearm causes extension (abduction) of the hand. 
The point of the article consists in a demonstration of the 
fact that, in spreading and folding the wing, the radius slides 
lengthwise along the ulna to a certain extent. Recapitulating 
certain points in the anatomy of the elbow and wrist, the author 
shows that this sliding is produced by the relative size, shape 
and position of the humeral surfaces with which the radius and 
ulna respectively articulate; these being such, that in flexion 
of the forearm the radial surface is nearest the wrist-joint, and 
in extension the ulnar one; and consequently the two bones of 
the forearm occupy different relative positions in flexion and ex- 
