22 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE 
therefore be easily traced and seen to be continuous along the whole length of the 
vertebral column. We have searched in vain for evidence of the “ occasional breaking- 
down” of the cuticular sheath (el. interna) in the vertebral regions as supposed by 
Zykoff for Siredon (Bull. Soc. Nat. Moscou, Bd. vii. 1893, p. 34). 
The main cells of the chorda do not undergo any marked change, but in the centre 
of each interseptal mass, at the point coincident with that of greatest flexibility, 
there has now arisen, apparently by accumulation of a fluid contents, a conspicuous 
globular vesicle (Pl. I. fig. 15, v.c.), which we propose to term the vesicula centralis, 
and assume to be in some way associated with facilitating the movements of the 
parts. 
Goette, by an ingenious argument, has drawn the conclusion (op. cit. p. 566), 
primarily from the study of the caudal region, that in Sphenodon the vertebre are not 
truly amphiceelous. He extends this conclusion with qualification to the trunk- 
vertebrae, which he figures as transmitting an uninterrupted notochord. Osawa has 
adopted his view and applied it to the vertebral column generally (98*. p. 104). 
We defer consideration of the caudal region, which is specialized on its own lines, till 
later, but acceptation of Goette’s view nevertheless depends entirely upon what we are 
to understand by an amphiccelous vertebra. As constituted in many bony fishes, this 
type of vertebra, at first sight solid, at its central and most completely constricted 
region, is inreality perforated by a minute aperture or canalis dicentralis, for transmission 
of a delicate thread-like process of the notochord connecting the adjacent inter- 
vertebral masses. If such be termed an amphiccelous vertebra, as is customary, the 
mere continuity of this notochord in Sphenodon would be no justification for dis- 
regarding the accustomed terminology under which its vertebrae are described as 
amphiceelous. If, on the other hand, by an amphiccelous vertebra be meant one 
centrally solid and with excavated extremities,—/. é., a vertebra of which one or both 
articular faces have not become condylar or flattened—then the term may be applied to 
Sphenodon, the peculiar characters of its vertebrae being in this case the great depth 
of its concavities. Inasmuch as we have shown the chordal plates to be notochordal 
derivatives, we agree with Goette, in a sense, as to the presence of a continuous 
notochord, which on the whole simplifies the customary conception of the Rhyncho- 
cephalian vertebra. If, however, for argument’s sake we dismiss the chordal plate 
with the rest of the chorda, the characters of the Sphenodon-vertebra become more 
nearly comparable to those of the cylindroidal type to which Credner has specially 
drawn attention in Paleohatteria (op. cit. p. 492), which may or may not have been 
plate-bearing. Viewed from this standpoint, the extension of Goette’s argument by 
Osawa, instead of supporting his defence of the supposed Agamid affinities of 
Sphenodon, weakens it to an unexpected degree. 
Passing now to the caudal region, the most important facts concerning the 
