94 HADROSAURUS. 
vex, but towards its inferior extremity forms a sloping plane directed obliquely 
inward, and jutting forward at its termination. 
The inner part of the shaft, Fig. 2, at the upper two-thirds is comparatively 
narrow and cylindroid. Below, it expands into a broad triangular plane directed 
somewhat backward, and rendered slightly concave transversely by the prominence 
of the anterior border, which ends in an angular, roughened process. 
The outer part of the shaft, Fig. 3, is cylindrical, with a broad, wing-like expan- 
sion curving backward at its upper extremity, and terminating in a wide, triangular 
surface at its lower extremity. 
The back part of the shaft, Fig. 4, is cylindroid at the middle, and rapidly 
expands above into a wide surface rendered transversely concave by the backward 
projection of the inner and outer portions of the head. At its lower third it rises 
into an acute ridge separating the inner and outer surfaces of the bone. 
The head of the tibia, Figs. 1-5, in front and at the sides together, forms a semi- 
circular outline. Its back part viewed from above exhibits three strong prominences. 
The inner two (Figs. 4, 5), nearly equal in size, form, and direction, constitute a pair 
of articular condyles separated by a deep notch. ‘The outer prominence is formed 
by a wing-like expansion of the external part of the shaft, and is separated from the 
condyles by a wide, concave notch. The articular surface of the head is nearly a 
horizontal plane at its fore part, but is convex posteriorly as it extends upon the 
three backward prominences. It is rough and deeply marked with vascular grooves 
proceeding from the back part. 
The tarsal articular surface, Fig. 6, has its long diameter in a reverse direction 
to that of the head of the bone. In outline it forms an irregular trapezium, with 
the short anterior side nearly straight and directed obliquely forward and inward, 
with the inner side gently sigmoid, the outer border deeply sigmoid, and the poste- 
rior shortest side straight and directed obliquely backward and forward. ‘The sur- 
face is somewhat rough. In the direction of its long diameter, or antero-posteriorly, 
it is for the most part concave, but is convex at the back extremity. In the direc- 
tion of its short diameter it is for the most part convex, but is depressed near the 
antero-internal angle. 
The interior of the tibia possesses a large medullary cavity. The orifice of the 
medullary nutritious canal is directed downward and is situated at the postero- 
external part of the shaft just above its middle. 
The measurements of the tibia are as follows :— 
Inches. Lines. 
Length of the tibia externally. é ; . : ; - . 36 9 
Length in front . : 35 
Circumference at Toa oat of the shaft, fone just fiSlow the 
middle. : g : : ; } ; 2 eel 8 
Breadth of the upper Sine ; : . : : ; pug li 3 
Diameter of middle of head antero- posteriorly 4 : . é aD) 6 
Breadth of tarsal extremity . : : Z ; A : - plo 
Diameter antero-internally . : : : : . : P ‘FD 10 
Diameter at middle of tarsal surface. : : : : : :aae2 10 
Diameter postero-externally : hic : : : c ae 4 
