ANNIVERSARY ADDRESS OF THE PRESIDENT. li 
large hind lobe, convex outwards and concave inwards, as in Paleo- 
therrum. The ulna is complete and much larger than in any of the 
Lquide, while it is more slender than in most of the true Palco- 
theria; it is fixedly united but not anchylosed with the radius. 
There are three toes in the fore limb, the outer ones being slender, 
but less attenuated than in the Hquidw. The femur is more like 
that of the Palcotheria than that of the horse, and has only a small 
depression above its outer condyle in the place of the great fossa 
which is so obvious in the Equide. The fibula is distinct, but very 
slender, and its distal end is anchylosed with the tibia. There are 
three toes on the hind foot having similar proportions to those on 
the fore foot. The principal metacarpal and metatarsal bones are 
flatter than they are in any of the Hquwde«; and the metacarpal 
bones are longer than the metatarsals, as in the Palwotheria. 
In its general form, Plagiolophus resembles a very small and 
slender horse*; and is totally unlike the reluctant, pig-like creature 
depicted in Cuvier’s restoration of his Palewotherium minus in the 
‘Ossemens Fossiles.’ 
It would be hazardous to say that Plagiolophus is the exact radical 
form of the Equine quadrupeds ; but I do not think there can be 
any reasonable doubt that the latter animals have resulted from the 
modification of some quadruped similar to Plagiolophus. 
We have thus arrived at the Middle Kocene formation, and yet 
have traced back the Horses only to a three-toed stock; but these 
three-toed forms, no less than the Equine quadrupeds themselves, 
present rudiments of the two other toes which appertain to what-I 
have termed the “ average” quadruped. If the expectation raised by 
the splints of the Horses that, in some ancestor of the Horses, these 
splints would be found to be complete digits, has been verified, we 
are furnished with very strong reasons for looking for a no less 
complete verification of the expectation that the three-toed Plagio- 
lophus-like ‘‘avus” of the horse must have had a five-toed “atavus” 
at some earlier period. 
No such five-toed “ atavus,” however, has yet made its appear- 
ance among the few middle and older Kocene Mammalia which are 
known. 
Another series of closely affiliated forms, though the evidence they 
afford is perhaps less complete than that of the Equine series, is pre- 
sented to us by the Dichobune of the Eocene epoch, the Cainotherium 
of the Miocene, and the Zragulide, or so-called “ Musk-deer,” of 
the present day. 
The Tragulide have no incisors in the upper jaw, and only six 
grinding-teeth on each side of each jaw; while the canine is moved 
up to the outer incisor, and there is a diastema, in the lower jaw. 
There are four complete toes on the hind foot, but the middle meta- 
tarsals usually become, sooner or later, anchylosed into a cannon 
* Such, at: least, is the conclusion suggested by the proportions of the skeleton 
figured by Cuvier and De Blainville; but perhaps something between a Horse 
and an Agouti would be nearest the mark. 
