Lect. VI.] A DRY SKULL. 153 



the expression "morphology of the skull" infinitely more 

 than that. I shall merely mention certain things 

 that have turned up in the course of several months' 

 steady work at these types ; especially showing how 

 far the Mole agrees with, or differs from, the Hedgehog, 

 in its development. In the earliest stages, these two 

 kinds are very similar in many respects, but some of 

 the most remarkable modifications of the part which 

 becomes the malleus take place in young Moles before 

 they leave the nest. There is a cartilaginous pterygoid 

 rudiment, as in the Hedgehog, and the basis-cranii is 



n^® 



FiQ. 14. — Embryo of Mole (Talpa eiiropcea), two views of head, 

 magnified 2 diameters (4th stage). 



pneumatic as in that type ; air-cavities like those seen 

 in Crocodiles and Birds being developed there. There 

 is an additional bony centre found in the manubrium or 

 handle of the hammer, besides the internal deposit of 

 bone formed in its head. But the perichondrial (or 

 outer) bone, answering to the external articular tract in 

 the lower jaw of the oviparous types, soon takes on a 

 very remarkable form ; it becomes idld-groion, so to 

 speak, and three sub-distinct parts can be traced. These 

 are seen to answer to the articulare externum, the supra- 



