67 
that of one side only is completely enclosed: the foramen lacerum 
posterius is very small; there is a distinct foramen glenoideum. In 
the Manis the characters of the foramina are very similar, but there 
is no canalis caroticus. 
In the Orycteropus Capensis the small optic foramen is placed back 
within the lamina enclosing the coalesced foramina spheno-orbitarium 
and rotundum, so that in a side-view it is concealed : just before the 
foramen ovale is an opening into the substance of the bone: the 
foramen lacerum anterius extends all along the anterior and inner 
side of the bone of the ear; the foramen lacerum posterius is of a 
roundish oval form; the foramen condyloideum is very large: there 
is neither a distinct canalis caroticus nor a foramen glenoideum. 
The Sloths have some peculiar characters of their own: in them the 
foramina opticum and spheno-orbitarium are distinct within, but the 
orbito-sphenoid sends out a little process forming a canal, which 
serves as the external opening for both of them ; the foramen rotun- 
dum is quite separate, opening at some distance below: in the Bra- 
dypus tridactylus it opens just at the point where the vertical lamina 
of the palatine bone joins the orbito-sphenoid ; the foramen ovale is 
also very close to the junction with the pterygoid. There is a distinct 
canalis caroticus, but no foramen glenoideum; the foramen condy- 
loideum is large and conspicuous. 
It is in the Pachydermatous and Ruminant orders, however, that 
I am enabled to show the clearest indications of accordance between 
certain characters of the foramina and the groups into which these 
orders are divided. In the elaborate and highly-interesting paper 
read not long since by Professor Owen before the Geological Society, 
in which he suggested the admirably-chosen names ‘ Artiodactyla’ 
and ‘ Perissodactyla’ for the two subdivisions of the Ungulate Mam- 
malia, it is much to be regretted that he has in no way alluded to 
the characters which the under surface of the skull presents; for 
they show three different types of structure, which, so far as those 
genera, of which the under surface of the skull is known, would indi- 
cate, appear very distinctly separable. Of these, two are included 
in the order Pachydermata, as usually adopted, while the third is 
that of the Ruminant. I am not at present prepared to offer any 
decided opinion as to the suggestion of Professor Owen, that the 
two orders ought to be united; and indeed that question forms no 
part of the present disquisition ; but in pointing out the characters 
presented by the cranium in these three distinct types, I cannot but 
very much regret that I have not been able to meet with skulls of 
any of the fossil genera that afford the intermediate links by which 
Professor Owen proposes to unite the orders, in such a condition as 
to enable me to discriminate the characters of the basal portion of 
the cranium. Perhaps the absence of such specimens may in some 
measure account for the omission of any notice of these characters 
in the paper to which I have alluded. 
In looking on the under surface of a Ruminant skull, the observer 
is at once struck with the great separation between the nidus of the 
last molar tooth and the walls of the canal of the posterior nares ; 
