76 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
specimen. In Pachyrukhos , the anterior bar is apparently regularly want- 
ing. The inferior arch supports a strong median tubercle. 
The axis (PI. II, figs. 23, 24) is not sufficiently well preserved in any 
of the specimens examined to show the shape of the spine. Unlike Pro- 
typotherium , the odontoid is strongly curved upward and the transverse 
processes are perforated by a large arterial foramen, which is quite small 
in Protypotkerium . The centrum is keeled interiorly and supports a pair 
of large tubercles at its posterior margin. 
Little can be said regarding the remaining cervicals, as in all the speci- 
mens available the transverse processes have been broken off, and in the 
majority of cases the neural spines also. In the third cervical (PL II, fig. 
22) the neural spine is low, broad and directed vertically. The centra of 
the third to the fifth cervicals inclusive are keeled interiorly, the keel 
becoming bifid posteriorly and terminating in a pair of tubercles. The 
transverse processes are perforated by a large arterial canal. 
A single lumbar vertebra, from which the transverse processes and the 
neural spine are missing (PI. I, fig. 7), is interesting in that it shows the 
strongly interlocking character of the zygapophysial articulations. Rather 
prominent metapophyses are present. Anapophyses are but slightly 
developed. The centrum is hour-glass-shaped, with prominent median 
keel. 
Appendicular Skeleton. — The scapula has not been preserved with 
sufficient completeness to warrant an attempt at extended description. 
Enough remains in one specimen to show the presence of a high spine 
and prominent metacromion. 
The humerus (PI. II, fig. 13) is of about the same size as the corre- 
sponding element in the larger individuals of Protypotkerium australe , 
but differs structurally in several important details. The shaft is strongly 
compressed laterally. The head is of about the same shape as in Pro- 
typotkerium , the greater tuberosity rising farther above the level of the 
head than in the latter genus. The lesser tuberosity is comparatively 
insignificant and is separated from the greater tuberosity by a wide bicip- 
ital groove. The area of insertion of the deltoid is broad and flat, the 
margins of this area converging distally to form a sharp ridge. Distally, 
the shaft expands transversely. The supinator ridge is somewhat better 
defined than in Protypotkerium and the inner epicondyle heavier. Capi- 
tellum and trochlea are differentiated to about the same extent as in Pro- 
