Zoological Society. 4Ai7 



wedge-bones, and represents only the inferior cortical part of such 

 body. The odontoid process of the axis is the central and main part 

 of the body of the atlas." (pp. 92, 93.) 



But in fishes these subvertebral processes coexisted with the par- 

 apophyses in the same vertebrae (Archetype, pi. 1. fig. 4. pp. 3, 4, 

 5, 6, &c.), and likewise with the haemal arches in the tail, with which 

 Dr. Melville contended that they were serially homologous ; in other 

 words, the homotypes. 



The caudal haemal arches in fishes were, however, manifestly 

 formed by other and true vertebral elements. Here Professor Owen 

 explained by diagramatic sketches the various ways in which the 

 haemal arch in the caudal vertebrae of fishes" was formed, as he had 

 described in his work. " The best marked general character of the 

 vertebral column of the trunk in the class Pisces is that which Pro- 

 fessor J. Miiller first pointed out, viz. the formation of the haemal 

 arches in the tail by the gradual bending down and coalescence of 

 the para])ophyses ; the exceptions being offered by the ganoid Poly- 

 pterus and Lepidostens and the protopterous Lepidosiren. The pleur- 

 apophyses are sometimes continued in ordinary osseous fishes from 

 the paraj)ophyses, after the transmutation of these into the haemal 

 arches. I'he dory, tunny and salmon yield this striking refutation 

 of the idea of the formation of those arches in all fishes, by displaced, 

 curtailed and approximated ribs. In some fishes, however {e. g. the 

 cod), reduced pleurapophyses coalesce with the parapophyses to 

 form the haemal arches of the caudal vertebrae." (p. 90.) 



•• Thus the contracted haemal arch in the caudal region of the body 

 may be formed by different elements of the typical vertebra, e. g. by 

 the parapophyses (fishes generally) ; by the pleurapophyses {Lepi- 

 dosiren) ; by both parapophyses and pleurapophyses {Sudis, Lepido- 

 stens) ; and by haemapophyses, shortened and directly articulated with 

 the centrums (reptiles and mammals)*." (p. 91.) 



The last conclusion was that which was now called in question, 

 or rather the sense in which Professor Owen here used the term 

 h^mapophyses was altered by Dr. Melville to the signification which 

 some anatomists expressed by the terms ' wedge-bones ' and subver- 

 tebral processes, and which Professor Ovren expresses by the term 

 hypapophyses. Professor Owen had concluded that as the haemal 

 arches in the tail of fishes were formed by more or less of the modified 

 elements of the more expanded haemal or costal arches in the abdomen, 

 the haemal arches in the tail of batrachians, saurians and mammals 

 were also formed by modifications of more or less of the expanded 

 haemal or sterno-costal arches of the trunk. 



The coexistence of the subvertebral or inferior processes of the 

 centrums (hypapoj^hyses) with the true haemal arches in fishes, 

 proved that these arches could not be the homotypes of these pro- 

 cesses in the tail any more than in the trunk ; and a conclusion so 

 established in fishes was good for batrachians, saurians and mammals. 



* By a misconception of the sense in which Professor Owen uses the terra 

 * haemapophyses,' M. Agassiz has applied it to the laminae of the inferior or haemal 

 arches in fishes. (Recherches sur les Poiss. Foss. torn. i. p. 95.) 



