466 
THE STRUCTURE AND RELATIONSHIPS OF ANCODUS. 
of the supraoccipital are less developed than in 0. Culbertsoni, more so than in (9. 
aracilU The upper margin of the bone is arched regularly from side to side and 
slightly notched in the median line. In this region, also, is considerable develop- 
ment of diploetic structure, separating the two tables of the bone. Even in young 
specimens it is by no means easy to determine the position of the sutures between 
the supraoccipital and the parietals; the former appears, however, to take part in 
the formation of the cranial roof to about the same extent as in Oreodon and otlier 
primitive artiodactyls. Comparatively little of the lambdoidal crest is formed by 
the occipital bones. 
The basisphenoid is a heavy, subcyliiidrical bone, shaped much like the basi- 
occipital, but narrower and with an uninterrupted ventral surface. Its junction 
with the presphenoid is concealed by the vomer. Both the basisphenoid and the 
basioccipital, aside from the large tubercles on the latter, have very much the liirin 
and proportions seen in Oreodon. The alisphenoid is well developed; its ascending 
jiortion is narrowed at the base by the foramen lacerum anterius and foramen ovule, 
which are placed quite near together, but above these it widens out. The ptery- 
goid process is stout, but of no great vertical height; it has the peculiarity of ex- 
tending to the auditory bulla, with which it comes in contact and thus encloses 
the foramen lacerum medium in a deep fossa. This is an unusual feature. The 
presphenoid is not visible, being covered up by the vomer, and the limits ol' the 
orbitosphenoid cannot be made out with certainty in any of the specimens. 
As in the primitive artiodactyls generally, the parietals are extremely long 
and make up most of the roof of the cerebral fossa. For the greater part of their 
length they unite to form a high, thin sagittal crest, which is gently arched from 
before backward, rising both from the forehead and the lambdoidal crest; anteriorly 
it bifurcates into twm low and slightly roughened temporal ridges. The parietals 
themselves likewise diverge at this point and receive between them a tongue-shaped 
pro ongation of the frontals. For most of their course the parietals are nari-ow, 
the arge size of the squamosals preventing any great expansion laterally. In H-ont 
Let rpTeLoilir™''’ 
“ *''‘*'*‘ P”' “*■ '™'l Of ‘I"-' “■■anial 
laLdliial "’“''S'" “P n-e 
dude! til neriotie f J 7 '7 exoccipital and squamosal almost entirely ex- 
slidit foS! skull, butinferiorly thetwoelements diverge 
^ the periotic is exposed 
process of the squamosal is closely appliertothV'" tubercle. The posttympanic 
below the tube of the auditory meal; The extends 
backward and is separated only by a narrow slf ^ strongly 
region of the skull is very silla^r indeed 7 n T ^ P‘>d tympanic. This 
gracilis, in which the postdennlrl • Oreodon and especiallv of O. 
w»,'. The "'7 «».. in d C„/- 
y large, extending nearly the full width of the xvgo- 
