92 ; HADROSAURUS. 
The posterior surface of the shaft (Fig. 4), less level than the outer, presents a 
conspicuous process, as in the /guanodon, springing from its middle internally, and 
calling to mind the third trochanter of certain Pachyderms, as the Horse and Rhi- 
noceros. An abrupt rising of the bone, extending from the process just mentioned 
towards the head and internal condyle, defines the posterior surface from the inner 
one. ; 
The internal and anterior surfaces (Figs. 1, 3), less defined from each other than 
the surfaces above described, together form a half section of a cylinder, which is 
antero-posteriorly compressed above where it sustains the head of the bone. The 
upper third of the anterior surface (Fig. 1) is transversely concave, arising 
from the presence of a strong process, springing from and defining its outer 
boundary. The process just mentioned, extending downward from the trochanter, 
gradually subsides and becomes continuous with two ridges, of which one forms 
the boundary between the anterior and outer surfaces of the shaft, while the other 
diverges in front to the lower third of the bone. The two ndges define three 
surfaces, giving origin to muscles corresponding with the triceps extensor of 
animals generally. Several inches below the commencement of the anterior ridge, 
to its inner side, is the orifice of a medullary nutritious canal, which is directed 
obliquely downward. 
The head of the femur (Figs. 1-5, a) partially overhangs the inner part of the 
shaft which sustains it. Its sides are exceedingly rugged, for the most part being 
rendered so by numerous vertical ridges and intervening grooves (Fig. 3, a). The 
articular surface is sub-circular and only moderately convex, or, as compared with 
its condition in animals generally, is in a remarkable degree flattened. It is quite 
rough, and is rendered so chiefly by branching vascular grooves (Fig. 5, a), of 
which the main one proceeds obliquely across the head from the interval anteriorly 
between the latter and the trochanter. 
The trochanter (Figs. 1-5, 6), when both condyles are brought to a level, rises 
above the head of the bone, than which it is more convex and broader antero- 
posteriorly, but is narrower transversely. It is separated in front and behind from 
the head by wide notches. Its back part (Fig. 4, 6) is roughened for muscular 
attachment. Its upper convex surface (Fig. 5, b) inclines inwardly, has quite an 
articular appearance, and is undefined from that of the head, with which it is con- 
_ tinuous by means of an isthmus. 
The condyles (Figs. 1-6, d, e), as usual, extend much more posteriorly than 
anteriorly. They are massive, with exceedingly rugged sides, especially that of 
the mner one (Fig. 3, d), being rendered so by vertical ridges and intervening 
grooves. ‘Their convex articular surfaces (Fig. 6) are conjoined by a narrow isth- 
mus, and are likewise rugged. 
In the absence of a well-developed patella, as in the recent Jguana, Cyclura, and 
their allies, there is no trochlear surface above the condyles in front. Occupying 
its position there exists a large oblique groove (Fig. 1, /) or depression communicat- 
ing with a short canal, which descends and expands in a funnel-like manner (Fig. 
6, /) between the articulating surfaces of the condyles. The borders of the funnel- 
like expansion are ridged and grooved in the same manner as the exterior sides of 
