322 REPORT—1846. 
too successfully in regard to the rising generation of anatomists; to be 
obscured. Ideas and statements are misquoted, unintentionally, doubtless, 
and through neglect of reference to the original work (as in the citation of 
the bones representing the bodies of the cranial vertebra in the Okenian 
theory): or they are misunderstood (as where the arches, neurapophyses or 
‘ bogentheile,’ composed as Oken truly said by the alisphenoids and orbito- 
sphenoids are held to be synonymous with the ‘ plaques protectrices’ of M. 
Vogt): the most extreme and least defensible views are selected out of each 
tentative step in the inquiry, and are clubbed together to represent the 
general result, which is of course dismissed with as sweeping a condemnation. 
The specific objections raised by Cuvier are deemed well-founded and un- 
assailable ; and to these M. Agassiz adds the following. Premising that, 
“the formation of vertebrae presupposes as a first condition the existence 
of a notochord* ;” and, arguing upon this basis, and on the assumption 
that the cephalic extension of the ‘ chorda dorsalis’ as it is permanently 
manifested in the Branchiostoma is not so great in the embryos of other and 
higher fishes, but is arrested at the region of the alisphenoid from the com- 
mencement of its development, M. Agassiz concludes: —“ Now, the application 
of this principle to the composition of the skull demonstrates at once that there 
exists but one cranial vertebra, the occipital vertebra, and that the rest of 
the skull is foreign to the vertebral system+.” 
At the period of development described and figured by M. Vogt in the em- 
bryo of the Coregonus, which period M. Agassiz conceives to represent the very 
earliest condition of the anterior extremity of the notochord, the pointed ex- 
tremity of the gelatinous central cells of this part terminates at the posterior 
boundary of the hypophysial space: but the peripheral capsule of the notochord 
extends over that space and forwards to the obtuse anterior extremity of the 
embryonal ‘ basis cranii’: and it is in the expanded aponeurosis, directly con- 
tinued from the chorda along the basis cranii, that the thin stratum of carti- 
lage cells are developed, arching along the sides of the hypophysial. space, 
from which the ossification of the basisphenoid, presphenoid and vomer 
proceeds {. 
The superaddition or the later continuation of the cylindrical gelatinous 
‘chorda’ in the aponeurotic basis of the cartilaginous and osseous growths of 
the vertebral centres in the trunk, seems to relate chiefly to their more or 
less cylindrical form in that region : the notochord regulates, asa mould, the 
course of ossification, disappearing by absorption as the bony lamelle of the 
vertebral bodies encroach upon it in their centripetal progress: the notochord 
plays an important part also in the establishment of the elastic jelly-filled 
capsular joints in the back-bone of fishes; and therefore it might well be 
dispensed with, or be early and rapidly removed, in the development of the 
flattened, expanded and anchylosed or immoveably articulated bodies of the 
cranial vertebra. And, besides, the notochord is immediately concerned in 
the development of only one of the elements of the typical segment of the 
endoskeleton. It is obviously, therefore, an unwarrantable and erroneous 
application of a developmental character, to conclude, from a modifica- 
tion of this one character in respect of a single element, the ‘ centrum,’ that 
every other character establishing the general homology of such element, as 
* “La formation des vertébres suppose, comme premiére condition, l’existence d’une 
* corde dorsale.’’’—Op. ci¢. tom. i. p. 127, livr. xviii. (1843.) 
+ “Or, V’application de ce principe 4 la composition de la téte nous montre d’entrée qu’il 
n’existe gwune seule vertébre crdnienne, la vertébre occipitale, et que le reste de la téte est 
étranger au systéme vertébrale.”—Jb. p. 127. 
+ Hunterian Lectures on Vertebrata, 1846, p. 71. 
