



455 



on the one hand, just as the neurapophysial cartilage is given off from it 

 on the other. 



If the haemapophysial cartilage becomes divided into rib and process, at 

 some little distance from the centrum, the rib is said to be attached to a 

 parapophysis ; and I believe that the only consistent definition that can 

 be given of a parapophysis is, that it is developed from the proximal end 

 of a hsemapophysial arch. 



If the paraphysis is merged in the general body of the vertebra, and 

 the rib becomes distinctly articulated close to it, the attachment of the 

 rib is said to be to the centrum. 



If the paraphysis is bent upwards, so as to pass insensibly in direction 

 into the neurapophysis, and becomes ossified in continuity with the latter, 

 the head of the rib is said to be attached to the neurapophysis ; although, 

 in truth, the head of the rib, or at any rate the proximal end of the 

 hsemapophysial arch of which that rib is a part, always retains, so far as 

 we have any evidence, its primitive connexion with its vertebral centrum, 

 into whatever new ones it may enter. 



If the neurocentral suture does not define the lower limits of a neur- 

 apophysis, and if the true definition of a parapophysis is that given above, 

 it is obvious that our nomenclature of the parts of the dorsal and lumbar 

 vertebrae throughout the vertebrate series, requires a thorough revision. 



To this subject I hope to return on a future occasion. 



VII. I subjoin the views of Vogt, and the criticisms of the late great 

 anatomist Johannes Miiller upon them, as the best means of exhibiting 

 their relation to those I have advocated. 



"If we ask ourselves what we mean by vertebrae, the primary segments 

 of the still indifferent tissue round the chorda, which arise in all vertebrate 

 embryos, are the first things to suggest themselves* These persist only in 

 the lowest grades of vertebrate animals, while in the higher they disap- 

 pear, in consequence of the more and more complete development of 

 secondary organs, especially of the extremities ; so far as we are able to 

 trace these segments, so far is there a formation of vertebrae. 



" But there is at once a difficulty, when we endeavour to find these seg- 

 ments in the rudiment of the skull of any vertebrate embryo. It is true 

 that many inflexions may be observed which appear to correspond with 

 such vertebrae, but unfortunately these do not appear in the same places in 

 different embryos ; and besides, these inflexions and curvatures of the base 

 of the skull are not in the least similar to the sharply and clearly defined 

 intervals between the primary vertebrae. The first of these intervals is 

 always formed behind the auditory vesicles, and lies therefore between 

 the occiput and the first cervical vertebra ; further forwards, as has been 

 said, no such interval is discoverable. But in the Cyclostome fishes, 

 which represent this embryonic condition, no vertebral divisions of the 

 skull are discernible ; in fact we have in the Myxinoids, only the chorda 

 with its sheath and muscular and cutaneous vertebral rings, which are 

 repeated up to the skull, but there cease. The skull of the Myxinoids, 

 like that of the higher cartilaginous fishes, cannot by any amount of 

 violence be forced under the vertebrate type. In the skull, then, the 



