Sinclair: typotheria of the santa cruz beds. 
93 
superior spines. The posterior inferior spine, and the ischial spine and 
tuberosity are also prominent. The symphysial portion of the pubis and 
the ischial ramus are broad, and the superior ramus of the pubis slender. 
The patella (PI. X, figs. 19, 20) is an almond-shaped element, convex 
in all dimensions anteriorly, while posteriorly it supports two equal concave 
facets for the femoral condyles. 
The femur (PI. X, fig. 8) is stout, with the shaft slightly arched anteri- 
orly, prominent minor, major and third trochanters, and heavy condyles. 
Except for the straighter shaft in Hegetotherium and the greater size, there 
is little or no difference between the femora of the two genera, the descrip- 
tion of that of Hegetotherium already given applying equally well to 
Pachyrukhos. 
Compared with the length of the femur, the tibia (PI. X, fig. 7) is pro- 
portionately much longer in Pachyrukhos than in Hegetotherium. This 
fact, correlated with the length and strength of the inner digits of the pes, 
the comparatively short fore limb and other structural peculiarities pres- 
ently to be mentioned, demonstrates in the writer’s opinion that Pachy- 
rukhos was a jumping animal. Tibia and fibula are firmly fused, both 
proximally and distally, the fusion at the distal end extending up the shaft 
for a distance somewhat greater than one third its total length. The tibial 
shaft is laterally compressed, with short, but sharp, cnemial crest. Inter- 
nally, the proximal portion of the shaft is convex and externally concave, 
and is slightly curved inward longitudinally, the nearly straight fibula 
forming the chord of the arc. The distal third of the shaft, formed by the 
fusion of tibia and fibula, is elliptical in cross-section. The proximal 
articular surfaces resemble closely the corresponding region in Hegeto- 
therium. They are approximately circular in outline, the inner trans- 
versely concave and antero-posteriorly slightly convex, and the outer 
convex in both directions. The spine is inconspicuous. The distal end 
closely parallels in structure the fused tibia and fibula of the rabbit. Both 
external and internal malleoli are long, the latter exceeding the former in 
this respect. Both are grooved posteriorly for transmission of tendons, 
the peroneal grooves being especially deep. The surface for the astragalar 
trochlea is similar in every respect to that in Hegetotherium and does not 
call for for separate description (see p. 79, and Pis. II, fig. 2 ; X, fig. 16). 
The American Museum is especially fortunate in possessing two skele- 
tons with the hind limbs complete and the elements of the pes in their 
