REVIEWS 755 
clavicle, to which the articulation of the coracoids has migrated and 
which is indistinguishably fused with the sternum proper. 
The sternum is a comparatively late development in reptiles. In 
the primitive reptiles there was none, not even a cartilaginous one. The 
coracoids in all primitive reptiles met or nearly met in the middle line, 
underlain in their whole extent by the posterior prolongation of the 
interclavicle. Back of the coracoids, occupying the interval between 
their divergent hind borders and reaching to the pelvis, the under side 
was sheathed by ventral ribs in the majority of forms, leaving no space 
for even the smallest cartilaginous sternum. This condition has been 
found so often and in such perfect preservation among American Permo- 
Carboniferous reptiles that there can be no doubt of the entire absence 
of the sternum in all forms. Just what was the origin of the sternum, 
and the cause of its appearance, are of course yet unproven, but it seems 
to the writer extremely probable that the sternum is nothing more nor 
less than modified sternal ossifications in the parenchymatous tissue, of 
the same nature as the more posterior ribs and originally a part of the 
same series. 
Evidence now seems conclusive that the plesiosaurs and ichthyosaurs 
are of very primitive origin, doubtless descended from terrestrial reptiles 
which had not yet acquired a sternum, and in which the coracoids met 
in the median line. 
That the coracoids of the pterodactyls should have formed an 
articulation on the interclavicle in the absence of clavicles and the 
presence of an ossified or cartilaginous sternum is an improbable theory 
without any evidence that the writer can see to sustain it. 
Mr. Hooley reaches some interesting conclusions as to the mechanics 
of the arm and forearm in Ornithodesmus, but which are not borne out 
by the American specimens of pterodactyls. He asserts that the radius, 
so far from its lying parallel with the ulna or in a pronated position, had 
acquired an over-supinated position, with its distal extremity on the 
dorsal side of the ulna. He also asserts that there was great freedom of 
movement in the carpus, not only dorsoventrally, but in an antero- 
posterior direction. With the arm extended and the elbow backward 
and the thumb in front, the humerus must necessarily occupy an oblique 
position or the radius is slightly pronated. With the radius crossing 
back of the ulna to the dorsal side, the palm of the hand would be 
turned forward. It is true that the wing metacarpal and the phalanges 
in their function of supporting the patagium have acquired an anomalous 
position in that the articulations have become antero-posterior instead 
