6 2 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



the dilated riblets at the root of the neck in living lizards, im- 

 mediately preceding those which join the breast-bone, more nearly 

 than any other skeletal elements with which I am acquainted ; but the 

 absence of any indication of bifurcation made me hesitate to con- 

 sider them such, because all the cervical and the foremost thoracic 

 ribs in Iguanodon have a forked vertebral end. If sternal, I should 



Pig. 17. — Shoulder -girdle of Iguanodon. (From M. Dollo's figure.) 



sc, the scapula ; cor, the eoracoid ; st, the sternum ; gl, the glenoid fossa. 



invert the base, and directing the narrow end downwards, regard 

 them as the homologues of xiphisternals only ; but to this hypothesis, 

 not less than to their supposed homology with the paired sternal plates 

 of Brontosaurus, there seem to me to be strong objections, notably the 

 absence of marks of costal attachments ; so that, upon a review of 

 all the circumstances, I think the balance of probabilities inclines 

 towards Prof. 0. C. Marsh's opinion that they are clavicles. To 

 the objection that had such a rhomboidal sternum as I have 

 imagined actually existed it must have been preserved, I would 

 reply that this presupposes that it must have been an osseous plate ; 

 but the analogy of Crocodilia shows that it might have been cartila- 

 ginous, and have perished with the rotting of the carcass, the epi- 

 sternum alone remaining ; and this is favoured by M. Dollo's dis- 

 covering between the coracoids and his xiphisternals (?) " une piece 

 osseuse, fusiforme et legerement bombee sur sa face centrale," which 

 he is himself disposed to regard as episternal ; for one can hardly 

 suppose it probable that the bony sternum perished while the epi- 

 sternum was preserved. 



