90 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 follows :— 
Inches. Lines 
Extreme length of the humerus 2. wt 2 5 : . 22 6 
Breadth at the tuberosities ; : : : : : - . 6 10 
Thickness at the head. : ant 3 
Breadth of shaft above the mateaitee or uct ibetare it serial to contract 
into the lower half oy) 4 
Thickness in the same position 5 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 penis 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 downward. One occupies the ridge beneath the 
head; the other 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 
Iguanodon have been discovered. In a slab of stone containing imbedded part of 
the skeleton of a young Jywanodon, known as the Maidstone specimen and preserved 
* in the British Museum, there are two bones described by Dr. Mantell 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, Pl, 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 . : : : : A : . 20 6 
Circumference at middle of the shaft ¢ , 4 : : Te 11 
Long diameter of the head 3 
Short diameter of the head F s ; F ‘ ong 6 
Long diameter of carpal end . F , : : - 5» 683 1 
Short diameter of carpal end 2 3 
1 British Fossil Reptiles, Dinosauria, p. 309. 
