CRANIAL CHARACTERS OF THE SNAKE-RAT, 69 
The circumstance which gives especial weight to this difference 
in the occipital foramina of the two skulls is that it involves a 
corresponding difference in the large nervous centre (the medulla 
oblongata) which occupies the foramen. I conceive that osteal 
characters or forms associated with corresponding modifications of 
any portion of the nervous system are of first-class importance. 
This would especially apply, in the case I am considering, to the 
Soramen magnum occipitale: the same principle would hold good, 
in a minor degree, as to the differences already mentioned in the 
infra-orbital foramina, which transmit the nerves distributed to 
the tactile organs about the mouth. 
Fig. 5. Fig. 6. 

Under view of Cranium of Snake- Under view of Cranium of Mus 
Rat, minus the lower jaw. En- rattus, minus the lower jaw. 
larged two diameters. Enlarged two diameters 
On the under surface of the skulls there are further distinctive 
differences. Inthe new rat the foramen ovale is hid by the lateral 
spreading of the pterygoid processes of the sphenoid bone ; in the 
Black Rat it is exposed. The breadth of the’ palate, the size of 
