THE STRUCTURE AND RELATIONSHIPS OF ANCODUS. 481 
trochlea is very prominent and massive and of asymmetrical shape, the inner 
border rising considerably higher than the outer. The condyles are large and pro- 
ject strongly backward, and are of unequal size, the outer one being distinctly the 
larger and more prominent. The strong backward projection of the condyles, and 
the great prominence of the trochlea in front give to this portion of the femur an 
unusual antero-posterior diameter. In other respects the femur resembles that of 
Oreodon^ except for its much greater size. 
In A. americanus the femur has a widely expanded and antero-posteriorly 
compressed proximal end. The head is rather small and set upon a short, but dis- 
tinct neck, dilfering much in appearance from the long, slender, and prominent neck 
of the femur figured by Kowalevsky. The head is far removed from the great 
trochanter, with which it is connected by a long, compressed bridge of bone. The 
great trochanter is high, rising somewhat above the level of the head, very deep 
antero-posteriorly, massive and rugose, with recurved posterior border. The digital 
fossa is deep but small, having but little extent either vertically or transversely, 
and there is no distinct ridge connecting the great and second trochanters. The 
shall is very long, slender, and rounded, not nearly so heavy as in A. brachyrhynchis, 
and is notably less massive distally. The condyles are much smaller and less 
prominent than in the latter species, the rotular trochlea less elevated and, conse- 
quently, the whole distal end is much less extended from before backward than in 
the last-named species. 
The patella is a remarkably large and massive bone, which may be described 
as being like the knee-cap of Oreodon with the addition of a long, broad, and thick 
tuberosity, which covers nearly the whole anterior face. The proximal surface is 
abruptly truncated and slightly concave, with raised anterior border. The antero- 
posterior diameter is greatest along this line. In its upper three-fourths the bone 
is of nearly equal transverse and fore-and-aft diameters, though the anterior iace is 
narrower than the posterior, while the distal portion narrows abruptly to form an 
incurved hook, which has hardly more than one-third the fore-and-aft depth of the 
rest. The articular surface is unequally divided by a ridge into two facets for the 
trochlea of the femur; transversely the two are of the same width, but the outer 
one has the greater height. The inner border of the internal facet is somewhat 
recurved, so as to slightly cover the mesial face of the femoral trochlea. The same 
feature occurs in Protoceras, but in a very much more marked degree. 
The tibia is considerably longer than the radius, much more so, proportion- 
ately, than in Oreodon, but in construction it is exceedingly like the tibia of that 
genus, though, of course, much larger and more massive in every way. The proxi- 
mal condyles are less oblique in position and less strongly convex in the antero- 
posterior direction; the spine is bifid and higher than in Oreodon and the groove 
dividing.it is deeper, but not so wide. The cnemial crest is very heavy and promi- 
nent, eSteiiding farther down the shaft than in Oreodon, and not terminating so 
.abruptly below: but sloping graduolly into the shaft, wlule proxima ly , tends m 
very in.assive and rugose surface for the attachment ol the patehar ligament, 1 
