456 



primary vertebral segments are wanting. However, they might be oblite- 

 rated by the early development of the organs of sense, or by the aberrant 

 development of the brain. 



"But there remains a second means of discovering the cranial vertebrae, 

 by examining the solid cartilaginous and bony basis of the skull ; though 

 here also we meet with insuperable difficulties. As the primitive type of 

 the more solid bodies of the vertebras, we have everywhere cartilaginous 

 rings arising out of the sheath of the chorda, and deposited around its 

 nucleus. Whether they arise as lateral halves or as entire rings, whether 

 they embrace the chorda completely or only above or below, is a matter 

 of no essential moment. But are such cartilaginous rings deposited 

 around the chorda, discoverable in the skull ? They will be sought for 

 in vain unless it be in the last, occipital, cranial vertebra; in this we 

 still find all the characters of a vertebra the investment of the chorda, 

 the chondrification in the sheath of the chorda. But the chorda does not 

 pass into the so-called first and second cranial vertebrae ; it invariably ends, 

 as Rathke justly states, between the auditory capsules, and never passes 

 into the body of the second cranial vertebra, let alone that of the first. 

 The lateral cranial trabeculae, which bear the two anterior cranial ver- 

 tebrae, can by no possibility be regarded as centra of vertebras, since in 

 this case, the characteristic feature, the being traversed by the chorda, 

 is entirely absent. Again, these lateral trabeculae are continued uninter- 

 ruptedly forwards, below the first division of the brain, showing no trace 

 of a median division. But in what part of the vertebral column has it 

 ever been seen that two vertebrae arise united and afterwards divide ? 



"It has therefore become my distinct persuasion that the occipital 

 vertebra is indeed a true vertebra, but that everything which lies before 

 it is not fashioned upon the vertebrate type at ally and that all efforts to 

 interpret it in such a way are vain j that therefore, if we except that ver- 

 tebra (occipital), which ends the spinal column anteriorly, there are no 

 cranial vertebrae at all." Vogt, Entw. d. Geburtshelferkrote, 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 vertebrae, and will 

 only admit an occipital vertebra, because the embryonic chorda, accord- 

 ing to Vogt's investigations, 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 investigation. That, however, the chorda in the 

 frog's larva extends beyond the base of 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 observa- 

 tions, 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 vertebrae, in the axis of the vertebral column, or those parts 

 which are developed from the chordal sheath alone, become finer and finer 

 anteriorly (although the column still exhibits vertebral divisions), and 



