M. Agassiz on Fossil Fishes. 337 



neither the one nor the other is possessed of true jaws. Now, 

 it will be observed that our most perfect fishes, such as the 

 salmon, have a period in their lives when they are at this 

 point of development ; only in the one this period is temporary, 

 a progress towards a state of higher development ; while in the 

 others it is the extreme term of development. These consi- 

 derations are of great importance in a philosophical point of 

 view, especially when we consider the application that may be 

 made of them to the other classes of the animal kingdom. 

 They have also served as a guide to our author in the rank he 

 assigns to the different families of fishes according to their 

 organization. 



The direction thus given to his studies necessarily led M. 

 Agassiz to discuss many questions of more general interest, 

 respecting which anatomists are not yet agreed. What he 

 says respecting the formation of the cranium appears to us 

 particularly interesting ; and no one, we think, can read the 

 following reflections without feeling their force. He says, — 

 " I have shared with a multitude of other naturalists the opi- 

 nion which regards the cranium as composed of vertebrae. I 

 am, consequently, in some degree called upon to point out the 

 motives which have induced me to reject it. This I shall do 

 the more freely, since we may now discuss the question in all 

 its aspects without fear of wounding the feelings of others. 



" M. Oken was the first to assign this signification to the 

 bones of the cranium. The new doctrine he expounded was 

 received in Germany with great enthusiasm by the school of the 

 philosophers ef nature. The author conceived the cranium to 

 consist of three vertebrae, and the basal occipital, the sphenoid, 

 and the ethmoid, were regarded as the central parts of these 

 cranial vertebrae. On these alleged bodies of vertebrae, the arches 

 enveloping the central parts of the nervous system were raised, 

 while on the opposite side were attached the inferior pieces 

 which went to form the vegetative arch destined to embrace the 

 intestinal canal and the large vessels. It would be too tedious 

 to enumerate in this place the changes which each author intro- 

 duced in order to modify this matter, so as to make it suit his 

 own views. Some went the length of affirming that the vertebrae 

 of the head were as complete as those of the trunk ; and, by 



