Zoological Society. 401 



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 Onjcteropus 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-sjihenoid 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 ; 



Ann. S^ Mag. N. Hist. Ser. 2. Vol. ni. 26 



