70 
molar series and the walls of the nasal cavity, yet in a rather young 
skull of Dicotyles labiatus, where the penultimate molar has not quite 
risen into its place, and the last remains still imbedded in its socket, 
there is on each side a narrow fissure between the posteriorly pro- 
jecting nidus and the pterygoid appendages; but this character can 
scarcely be reckoned among some others which do seem to approxi- 
mate the Peccary to the Ruminants, since the fissure is great even 
in the adult Ruminant, and in no adult member of the Pachyderma- 
tous order does the termination of the molar series extend back so 
far as to reach the anterior termination of the pterygoid appendage. 
It is in the occipital bone that the Peccary departs most from the 
character usual in the Hog-tribe, and approaches to that structure 
which is presented by the Ruminants, and by the other large group 
of Pachydermata. The origin of the paroccipital processes and the 
absence of the ridges extending inwards from their bases, together 
with the position of the foramen condyloideum, approximate the 
genus to the last-mentioned groups; but the processes themselves, 
although they are short, approach nearer in form to those of the 
Hogs. The lateral expansion of the pterygoid processes, although 
still considerable in Dicotyles labiatus, is much reduced in the Tajacu. 
The glenoid cavity is not pushed back to the same extent as in the 
Hogs, and its level is relatively much lower than either in them or 
in the Ruminants, so that a line drawn through the posterior termi- 
nations of the articulating surfaces would pass through the auditory 
bullz near their lower surfaces; and the structure of the glenoid 
cavity itself is quite distinct, somewhat resembling that so charac- 
teristic of the order Carnivora. It is an oblong surface, lengthened in 
a direction slanting from behind forwards and outwards, and is con- 
cave in the antero-posterior direction. The Hippopotamus shows 
itself to be closely allied in the structure of the occipital bone and of 
the glenoid cavity: the pterygoid bone is not sufficiently developed 
to form the inner wall of a fossa*. 
In both divisions of the artiodactyle Pachydermata the foramen 
ovale is not completed by the ali-sphenoid behind, but truly merits 
the name of a “ foramen lacerum” : there is no trace whatever of the 
ali-sphenoid canal, nor of the canalis caroticus, nor, in the true Hogs, 
of the foramen glenoideum ; this however exists, but is very small in 
the Peccary, in which also the position of the foramen condyloideum 
differs from that of the true Hogs in a degree corresponding to the 
altered structure of the occipital bone. 
The third great type of Ungulated Mammalia (the Perissodactyla 
of Professor Owen) is also marked as distinctly by the conformation 
of the base of the skull, as by that characteristic structure of the 
tarsus which enables the paleontologist, on looking only at an astra- 
galus, to recognize ‘“‘the armed Rhinoceros”’ as readily as if the 
animal complete were presented to his view. The skulls of the Horse, 
the Tapir, and the Rhinoceros, when we look on their under surfaces, 
* In an excellent skull of this animal contained in the Society’s collection, the 
lacrymal bone forms within the orbit a considerable osseous bulla, having thin 
parietes, and apparently destined for the protection of the lacrymal sac. 
