260 REPORT—1846. 
In the Fistularia tabaccaria the four anterior vertebra are much-elongated; 
the second one even to eight times the length of the ordinary abdominal ver- 
tebree: and their centrums are firmly interlocked together, by very deeply 
indented sutures, The parapophyses are co-extended with the centrums, and 
overlap each other, forming a continuous outstanding horizontal ridge on each 
side ; and the neural spines form a similar vertical continuous crest. 
In the Cobitis fossilis and C. barbatula the par- and pleur-apophyses of 
the second and third vertebrz coalesce and swell out into a large ‘ bulla ossea’ 
on each side, inclosing the small air-bladder of these fishes: they also lodge 
the little ossicles which bring this vertebral tympanum into communication 
with the prolongations or atria of the labyrinth *. 
In a large South American siluroid fish, I found the fore-part of the verte- 
bral column of the trunk apparently formed by one large vertebra, the body of 
which sent a broad triangular plate outwards on each side, giving it a rhom- 
boidal figure, viewed from below: these plates in this fish support and coalesce 
with five parapophyses, which ascend and increase in breadth as they approach 
the skull, where they join the paroccipitals, as they are, themselves, joined to- 
gether so as to form a continuous broad oblique outstanding plate of bone. 
Above these, the continuous bony neural arch is perforated for the exit of five 
pairs of nerves; the dorsal and ventral roots escaping separately, as in the 
sacrum of birds. The coalesced neural spines send up a lofty pointed plate 
to the overhanging supraoccipital. On vertically bisecting this specimen, I 
found the central parts of the bodies of five vertebrae, which had been deve- 
loped in the notochord, distinctly marked out, and preserving in their an- 
terior and posterior deep concavities the persistent gelatinous remains of the 
notochord; although the rest of the circumference of such centrums were 
anchylosed to the cortical or peripheral parts developed from the capsule of 
the notochord, viz. to the continuous expanded plate of bone below, to the 
parapophyses laterally, and to the neurapophyses above. The body of the 
first vertebra, or atlas, presented the exception of being quite detached from 
its elevated parapophyses, as well as from its neural arch ; it was anchylosed 
only to the bony plate below. The body of the second vertebra was six times 
as long as that of the atlas: yet the apices of the two deep terminal jelly- 
filled cones extended to and met in its centre. The bodies of the third and 
fourth vertebrz were elongated, but less so than that of the axis: the body 
of the fifth vertebra was singularly modified; its anterior half presenting the 
long and slender character of the antecedent vertebre ; whilst the posterior 
half was suddenly shortened, but extended in depth and breadth so as to 
adapt its shallow posterior concavity to that of the short and broad body of 
the first free vertebra of the trunk, which is followed by others of similar 
character. I have seen few better instances of adherence to type, irrespective 
of obvious function, than the persistence of the biconcave articular cavities, 
with the elastic capsules and contained fluid, in the centrums of these five 
rigidly fixed anterior vertebrz of the siluroid fish. 
The continuous bony plate supporting those centrums was perforated 
lengthwise by the aorta, offering another mode of formation of a hzemal canal, 
viz. by exogenous ossification in and from the lower part of the outer layer 
of the capsule of the notochord: the carotid hamal canal in the necks of 
birds seems to be similarly formed; and the neck of the ichthyosaurus derives. 
additional strength and fixation from apparently detached developments of 
bone in the lower part of the capsule of the notochord, at the inferior inter- 
space between the occiput and atlas, and at those of two or three succeeding 
cervical vertebre f. 
* Weber, G. H., De Aure et Auditu Hominis et Animalium, 4to. 1820. 
+ Sir Philip de M. Grey Egerton, in Geol. Trans. 2nd ser. vol. v. p. 187, pl. 14. 
