408 ON A NEW SPECIES OF MACRAUCHENIA (M. BOLIVIENSIS) 
and backwards at a right angle with its previous inclination into the 
occipital crest. 
This crest is nearly o'2 inch thick at the sides, and becomes still 
thicker in the middle line, where it joins the sagittal crest. It is 
II inch in diameter at its widest part, and about half an inch high. 
Its contour is that of a parallelogram, with its angles rounded off, 
and the middle of its upper side rather truncated. The lateral 
portions project backwards rather more than its centre ; so that, while, 
supposing the basi-occipital to be horizontal, a vertical line drawn 
through the posterior edge of that bone would nearly coincide with 
the contour of its central part, it would pass a little anterior to the 
plane of the lateral extremities of the crest. Inferiorly, the thick 
lateral portions of the crest divide into two ridges; the posterior 
of which turns slightly inwards and comes to an end, while the 
anterior, much sharper at its edge, passes forwards and outwards, and 
becomes continuous with the sharp ridge in which the paramastoid 
process terminates externally. 
Behind this ridge, between the paramastoid process, the occipital 
condyle, and the lateral convexity of that part of the occipital bone 
which lies above the foramen magnum, there is a deep fossa, which is 
divided into two portions by a transverse ridge, extending from the 
outer and upper part of the condyle to the posterior and inner 
face of the paramastoid process. The large precondyloid foramen 
(probably somewhat enlarged accidentally) opens into the lower and 
anterior division of the fossa, beside the condyle, and about }th of 
an inch behind its anterior inferior boundary. The upper boundary 
of the foramen magnum is almost straight, and its summit is below 
the level of the superior edge of the condyle (when the base of the 
skull is horizontal). The condyle is divisible into an upper, smaller, 
obliquely ascending, and a lower, more nearly horizontal facet. The 
line of junction between the two, forming the posterior limit of the 
condyle, is rounded off and is directed obliquely outwards and up- 
wards. The moderately convex upper facet looks upwards, back- 
wards, and but very slightly outwards. It is broad above, where its 
transverse diameter amounts to nearly half an inch, ana tapers off 
gradually to a point below and internally. 
The inferior facet, less curved than the other, is 0°6 of an inch 
wide behind, hardly more than half that in front, and fully o'8 of an 
inch long. It is slightly convex from side to side, and from behind 
forwards, posteriorly, where it looks downwards and outwards ; convex 
from side to side, and slightly concave from behind forwards, in front, 
where it is directed more horizontally downwards. Its anterior narrow 
