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tliat the spinal-nerve is always sitiialeti in tlie cranial half of ihe 

 solei'Otome to wliicli it belongs, that tlie first cervical-nerve does not 

 belong to the semi-segments from which the atlas is constrncted, at 

 least not, it' we maintain that the atlas is eqnivalent to the other 

 vertebrae and that its formula is SI^ -\- SUa. If now the 1'" spinal- 

 nerve is situated in the cranial semi-segment hi, as is in every 

 respect confirmed by investigation, then a fortiori the ponticulus 

 lying cranially from this nerve must be reckoned to the same semi- 

 segment, at all events most certainly not to the caudal semi-segment 

 lb. If consecpiently a ponticulus is present, then it follows necessarily 

 from the fact, tiiat the ponticulus has been formed in the cranial 

 semi-sclerotome la (it remains separated from Ihe caudal half of the 

 last sclerotome of the cranium by the cranio-vertebral interval 

 situated intersegmentally) that indeed Ihe atlas is no longer equivalent 

 to the other vertebrae, but is constructed instead of 3 semi-sclerotomes 

 and not of 2 and consequently the formula must run : SIa-|-SI6-|- SIK/. 



Hereby an answer is given both to the question put by de Burlkt 

 after the signification and the origin of the ponticuli posteriores and 

 laterales, occurring with man as a variation and with many mammals 

 constantly, and in the first instance to the question formulated in 

 the beginning of this communication, if activation can occur of the 

 osteogenetic potency of the "free" semi-segment h/. and if so, to what 

 phenomena this activation will give rise. 



The answer to Ihe first question must be that, on account of the 

 existence of the Ponticuli posteriores and laterales, the atlas may 

 most decidedly not be called equivalent to the other vertebrae, but 

 that, in comparison with the other vertebrae, it has enlarged itself, 

 as was likewise supposed by de Burlet by assimilation of a cranially 

 lying element originating in the semi-segment \a. 



The answer to the second question must be, that activation 

 of the osteogenetic potency of the semi-segment la is doubtlessly 

 possible, and that one of the phenomena, by which this activation is 

 characterized, consists in the occurrence of the ponticuli posteriores 

 and laterales, which limit cranially the foramina arcualia and 

 alaria. We can imagine this process thus, that in that region of 

 the semi-segment la, that corresponds with the arcus posterior 

 vertebrae (the region of the body of the vertebra remains for the 

 present out of discussion) on account of the influence of the ossi- 

 ficating potency existing in it, an osseous arch is formed, be it 

 usually only weak, which assimilates with the arcus posterior atlantis 

 and leaves, when doing so, a necessary opening for the passage of 

 the n. cervicalis I and the a. vertebralis, the foramen arcuale. The 



