Zoological Society. 447 
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 vertebre (Archetype, pl. 1. fig. 4. pp. 3, 4, 
5, 6, &c.), and likewise with the hemal arches in the tail, with which 
Dr. Melville contended that they were serially homologous ; in other 
words, the homotypes. 
The caudal hemal 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 
heemal 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. Miller first pointed out, viz. the formation of the hemal 
arches in the tail by the gradual bending down and coalescence of 
the parapophyses; the exceptions being offered by the ganoid Poly- 
pterus and Lepidosteus and the protopterous Lepidosiren. ‘The pleur- 
apophyses are sometimes continued in ordinary osseous fishes from 
the parapophyses, after the transmutation of these into the hemal 
arches. ‘The dory, tunny anc 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 hemal arches of the caudal vertebre.’’ (p. 90.) 
‘* Thus the contracted hamal 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- 
steus) ; and by hemapophyses, 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 
hemapophyses was altered by Dr. Melville to the signification which 
some anatomists expressed by the terms ‘ wedge-bones’ and subver- 
tebral processes, and which Professor Owen expresses by the term 
hypapophyses. Professor Owen had concluded that as the hemal 
arches in the tail of fishes were formed by more or less of the modified 
elements of the more expanded hzemal or costal arches in the abdomen, 
the hzmal arches in the tail of batrachians, saurians and mammals 
were also formed by modifications of more or less of the expanded 
hemal or sterno-costal arches of the trunk. 
The coexistence of the subvertebral or inferior processes of the 
centrums (hypapophyses) with the true hemal 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 term 
‘hamapophyses,’ M. Agassiz has applied it to the lamin of the inferior or hemal 
arches in fishes. (Recherches sur les Poiss. Foss. tom. i. p. 95.) 
