LECT. V.J THE HEDGEHOG'S SKULL. 137 



.a single, distinct, lateral piece. This might be con- 

 sidered to be a very small thing of itself, but many 

 grains make a heap, and facts of this sort, as to 

 exceptional characters, now accumulating, are be- 

 coming very numerous indeed. Where the maxil- 

 laries and palatines meet in the hard palate, there 

 these bones are deficient to some extent, as in the 

 Marsupials. Above these, toward the mid-line, the 

 vomer and its companion bones are remarkably well 

 developed in relation to the large Jacobson's organs, and 

 so are the retral tracts of the alse nasi, or cartilages of 

 the snout, that encapsule those remarkable organs. 



As in the Bird and Eeptile, the pituitary space is 

 open ; that is to say, the seat of the turkish 

 saddle has a round hole through it. As a rule, the 

 Mammalia agree with the cartilaginous Fishes and Frog3 

 in having this part filled in with cartilage. The air- 

 galleries into which the drum-cavities open in the 

 Crocodile and the Bird are represented here by a large 

 lateral recess, right and left, the basi-sphenoid giving 

 off a large, hollow wing, which takes the place of the 

 distinct India of the Cat. Among the various modifi- 

 cations found in the Insectivora this is one of the most 

 constant, but it is not universal. In the embryo Hedge- 

 hog, before any superficial bones are drawn towards the 

 cartilaginous skull as its support (a state of things like 

 that which is permanent in cartilaginous fishes), the deep 

 cartilages forming the lower jaws are very solid for a 



