'6o6 ON THE THEORY OF THE VERTEBRATE SKULL 



indeed a true vertebra, but that everything which lies before it is not fashio7ted 

 upon the vertebrate type at all, and that all efforts to interpret it in such a way are 

 vain ; that therefore, if we accept that vertebra (occipital), which ends the spinal 

 column anteriorly, there are no cranial vertebrss at all." — Vogt, Entzv. d. Geburt- 

 shelferkrote, pp. 98-100. 



" Vogt, and in the present work Agassiz also, contest the justice of the theory 

 of the composition of the skull of several vertebrse, and will only admit an 

 occipital vertebra, because the embryonic chorda, according to Vogt's investi- 

 gations, extends no further in the skulls of fishes and Amphibia. In this, in 

 my opinion, too much stress is laid upon a single result of embryological investi- 

 gation. That, however, the chorda in the frog's larva extends beyond the base ot 

 the occiput, further than where the slight trace of the basioccipital is ultimately 

 formed, I have myself seen. Even the anterior part of the vertebral column of 

 the Rays shows that the chordal system, out of which, according to my own 

 and Vogt's observations, only the central part of the fishes' vertebra proceeds, 

 may be abortive, whilst the cortical part of the vertebra, which arises in quite a 



■different way, is at its maximum of development. In a longitudinal section of the 

 anterior part of the vertebral column of a Ray, it is seen that the central parts 

 of the vertebrse, in the axis of the vertebral column, or those parts which are 

 developed from the chordal sheath alone, become finer and finer anteriorly (al- 

 though the column still exhibits vertebral divisions), and at last cease entirely, 

 without reaching the anterior end of the vertebral column. On the other hand, 

 Branchiostonia lubricum shows us the opposite extreme ; the chorda passes beyond 

 the anterior end of the skull, beyond the mouth and the eyes, far into the extremest 

 end of the snout. 



" This remarkable fact, first observed by Sundevall, was very surprising to me, 



.since in consec|uence of my studies up till that time, I regarded the existence of 

 three vertebrae in the proper cerebral cranium as certain, at least I considered the 



. assumption of a fourth ethmoidal vertebra to be uncertain and undemonstrated. 



" For now I saw at once, that it was undoubtedly possible that the cephalic 

 vertebral column might extend further forwards. There need not always be three 

 cranial vertebrae developed in the head ; in birds, reptiles, and fishes, the most 

 anterior vertebra is abortive, and is even entirely wanting in some families ; but, 

 in the Matnmalia and man, three cranial vertebree are without exception discover- 

 able in the basis cranii, either in the foetus, or in many cases even in young or 

 middle-aged animals — the occipitale basilare, sphenoideum basilare, posterius and 

 anterius ; these also occur in fish. How far the chorda primitively extends in 

 Mammalia is not yet made out ; but even although it should not reach through 

 the whole basis cranii, this, from the reasons which have been stated, would be no 

 good argument." — J oh. Miiller, Bericht. cclxviii-ix., MuUer's Archiv, 1843. 



END OF VOL. L 



