The central portion lies between the lateral cartilages and immediately under the coronary cushion.
These extend downwards from the lower border of the coronary cushion to the inferior margin of the os pedis.
They here affect the wall just where the bevel in it for the accommodation of the coronary cushion has rendered it weakest.
The main portion of the wall is developed from the numerous papillæ covering the corium of the coronary cushion.
Attention should then be given to the flap of skin and coronary cushion.
The coronary cushion is also affected in the same way, where the changes are noted most in its posterior portions.
It terminates in the coronary cushion and the sensitive laminæ.
This should run immediately under the coronary margin of the wall, and should stop short of injuring the coronary cushion beneath.
Repair after this operation is rapid, and takes place both from the exposed podophyllus membrane and from the coronary cushion.
It only remains to state that, like the coronary cushion, the surface of the sensitive frog is closely studded with papillæ.