THE WASA.TGH FAUNA. 
277 
especially seen in its small size. The mandibular ramus of the Oxymna 
forcipata is about the size of that of the Jaguar, but the brain, even with its 
large olfactory lobes, is onl}^ about two-thirds as long and one-third as wide. 
I have already described the brain of Corypliodon"^ as the lowest and 
most reptile-like Mammalian brain known, for the following reasons:—The 
diameter of the hemispheres does not exceed that of the medulla, which is 
as wide as the cerebellum. The latter is small and flat. The middle-brain, 
is the largest division, much exceeding the hemispheres in size, being espe¬ 
cially protuberant laterally. The hemispheres contract anteriorly into the 
very stout peduncles of the olfactory lobes. These continue undivided to 
an unusual length, and terminate in a large bulbus, which is at first grooved 
above and then bifurcate at the extremity. The length of the hemispheres 
is one-fifteenth that of the cranium, and their bulk one twenty-seventh that 
of the hemispheres of a Tapir of the same size. Their surface is not con¬ 
voluted, and there is no trace of Sylvian fissure. The region of the pons 
varolii is very wide, and exhibits a continuation of the anterior pyramids. 
The large size of the middle brain and olfactory lobes gives the brain as 
much the appearance of that of a Lizard as of a Mammal. 
The grade of a Mammalian genus is expressed in the skeleton by the 
structure of the limbs and that of the dentition. In the former, it is seen 
in the movable and in the fixed articulations, and the numbers of the digits. 
The movable articulations are those of the shoulder, elbow, wrist, hip, 
knee, and ankle. The fixed articulations are those of the ulna and radius, 
tibia and fibula, and those between the carpal and tarsal bones respectively. 
If we compare the limb-bones of the Eeptiles with those of the Mammals, the 
characteristic peculiarity of the former is seen in the absence of the crests 
which, in the latter, bound or divide the articular surfaces, or condyles; 
thus giving the joint greater firmness, and the movement greater precision. 
There are great differences in the development of these characters in the 
Mammalia, and the facts presented by the types of the Eocene are of con¬ 
siderable interest. 
In the Mammalia with most specialized limbs, the condyles f of fhe 
* Vide supra, p. 199. 
tin the present work, this term is used for the distal articular portions, not (as 
in anthropotomy) for the distal tuberosities, or epicondyles. 
