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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. 
Arriving thus at the demonstration, that the hemal arches in the 
tails of the air-breathing Vertebrata were formed like those in fishes, 
by a modification of the true hemal arches of the trunk, the question 
remained to be decided, which of the elements of such arches were 
continued into the caudal region of reptiles, cetacea, &c. in order to 
constitute those arches; and Professor Owen had shown that the 
solution was given by the adult perennibranchiate batrachia and by 
the immature crocodiles, in which diapophyses and pleurapophyses 
coexisted with such hzmal arches in the tail: the lamine of these 
arches therefore must be the hemapophyses as defined in his diagrams 
of the typical vertebra, and consequently they must be the homo- 
types of those hemapophyses which had received in the trunk the 
special names of ‘ischia,’ ‘pubes,’ ‘abdominal ribs,’ and ‘ sternal 
ribs.’ But the sternal ribs coexisted in the same vertebra with the 
inferior exogenous processes from the centrum, to which processes 
Dr. Melville proposed to transfer Professor Owen’s name of ‘ hem- 
apophyses.’ Professor Owen had, however, proposed a proper name 
for these commonly exogenous growths from the cortical part of the 
centrum, as he had likewise found himself reluctantly compelled to 
do for analogous exogenous processes from the neural arch, which 
were independent of and superadded to the ordinary ‘ diapophyses’” 
and ‘ zygapophyses.’ Professor Owen called the attention of Dr. 
Melville to a series of drawings in which he had proposed to illustrate 
his descriptions of these accessory processes, and alluded to his de- 
scription of them in the Catalogue of the Royal College of Surgeons. 
Professor Owen finally dissented from the definition of the ideal 
vertebra, which Dr. Melville had adopted from his friend Mr. Mac- 
lise. 
Professor Owen considered that a typical structure might be de- 
parted from hy excess as well as deficiency. Asan example of such 
excess, he regarded those vertebrze which, in subserviency to muscular 
attachments, developed hypapophyses, anapophyses, metapophyses 
and diapophyses, or which in like adaptive subserviency to stronger 
union developed epizygapophyses, in addition to the ordinary pre- 
and post-zygapophyses; or which developed from the upper part of 
the centrum epi-apophyses, which in the cranial vertebra had received 
the special denomination of clinoid processes, and were for the spe- 
cial protection of an appendage to the neural axis. In certain human 
crania these latter exogenous developments actually formed a secon- 
dary and minor neural arch internal to or concentric with the larger 
and normal neural arch; and Professor Owen drew a diagram of a 
section of such a vertebra, showing the small neural canal close above 
the centrum (basisphenoid) of the parietal vertebra, answering to, or 
homotypical with, the small hemal canal formed by exogenous 
growths from the under part of the centrum (basi-occipital) of the 
