124 ON THE MORPHOLOGICAL CONSTITUTION OF 



In the reptile both the ethmoidal and presphenoidal (?) * 

 sclerotomes are evacuated by the neural axis, the olfactory 

 nerves alone passing along in the compressed tubular, partially- 

 catacentric neural chamber of the latter — the olfactory capsules 

 occupying the right and left chambers of the former. In 

 reptiles, however, the very varied forms assumed by the bones 

 of the face, and more particularly by those of the palatine 

 arch, in relation to the nostrils, and the arrangements for 

 mastication, produce numerous remarkable modifications of 

 these two sclerotomes. 



In passing from the reptile to the fish, the ethmoidal 

 sclerotome may be said to gather together its scattered elements, 

 and to present a centrum and neural arch frequently as com- 

 pact as the human, but modified by the deficiency of nostrils, 

 and by the withdrawal of the neural axis. 



Ethmoidal Centrum and Neural Arch in the Mammal. — 

 The human cranium, as the most perfect in the higher of the 

 two forms of skull, will not unfrequently be found to afford a 

 clue to the signification of bones which, being only applied to 

 their final purposes in it, are more or less masked in the other 

 mammalia, and apt to be misunderstood altogether in the fish, 

 reptile, and bird. If we examine in connection the two bony 

 masses, which, in the current nomenclature of human anatomy, 

 are distinguished as frontal and ethmoid, they will be seen to 

 constitute a ring, the space within which is greatly dilated 

 behind, in consequence of the vast expansion, more particularly 

 of the upper and lateral portions of the frontal, while it is 

 diminished to a tubular chink in front, and is so indistinct 

 towards the nasal fossas that the older anatomists named it 

 " foramen caecum." (?) The development of this bony ring 

 shows it to consist of five pieces. These are — the mesial plate, 

 including the crista-galli of the ethmoid, the lateral masses of 



* This and the succeeding marks of interrogation we have found in a copy 

 annotated by the author. — Eds. 



