(JO HADROSAURUS. 



tion. The border of the deltoid expansion is convex, and is roughened below for 

 muscular attachment. 



The condyles are conyex and rough, and are separated in front by a notch expand- 

 ing upward into a broad concavity of the shaft ; behind they are separated by a 

 wide groove extending upward and disappearing upon the shaft. 



The latter, which was broken across in the specimen in two positions, exhibited a 

 large medullary cavity. 



The measurements of the bone are as foUows : — 



Inches. Lines. 



Extreme length of the humerus 22 6 



Breadth at the tuberosities ........ 6 10 



Thickness at the head ..,......' 3 3 



Breadth of shaft above the middle, or just before it begins to contract 



into the lower half . 5 4 



Thickness in the same position ....... 2 4 



Breadth of cylindroid portion of the shaft 3 2 



Circumference of cylindroid portion of the shaft .... 9 6 



Thickness of cylindroid portion of the shaft 2 9 



Breadth at condyles 5 



Diameter of head 2 6 



Antero-posterior diameter of inner condyle ..... 3 6 



Antero-posterior diameter of outer condyle. ..... 3 



Two orifices for medullary nutritious arteries exist on the posterior inner aspect 

 of the bone, both being directed doAVUAvard. One occupies the ridge beneath the 

 head ; the othei is on the inner border of the shaft just above the middle. 



The bones of the forearm of Hadrosaurus are not remarkably different in form 

 from those of the living Iguana. No adult bones of the forearm of the congeneric 

 Igiianodon have been discovered. In a slab of stone containing imbedded part of 

 the skeleton of a young Iguanodon, known as the Maidstone specimen and preserved 

 in the British Museum, there are two bones described by Dr. ManteU as metacar- 

 pals, but which are considered to be the radius and ulna by Prof. Owen, who 

 remarks that " they offer few differences worthy of notice except their greater 

 relative strength from the corresponding bones of the Iguana."^ 



The radius. Fig. 6, PI. XIV, has a compressed cylindroid shaft elevated into a sub- 

 acute ridge postero-externally for the attachment of an interosseal membrane. Its 

 upper extremity expands into a head, with a rough margin, supporting a semicircu- 

 lar roughened, brachial articular surface, which is slightly concave in its longer 

 diameter, and nearly level in the opposite direction. The lower extremity widens 

 in a clavate manner, presents a broad groove postero-internally, and ends in a convex 

 articular carpal surface. The measurements of the bone are as follows : — 



Inches. Lines. 



Extreme length of the radius 20 6 



Circumference at middle of the shaft 5 11 



Long diameter of the head .3 8 



Short diameter o£ the head 2 6 



Long diameter of carpal end ..... . . 3 1 



Short diameter of carpal end ........ 2 3 



' British Fossil Reptiles, Dinosauria, p. 309. 



