SOME PARTS OF THE SKELETON OF FISHES 275 
(whose origin is wrongly placed in the Cretaceous period, since it 
certainly took place much earlier, in the Jurassic epoch), also pos- 
sess an imperfect vertebral column. No inconsiderable portion of 
the end of the chorda remains without developing vertebre through- 
out the whole life of the fish, and becomes hidden under a roof- 
like arrangement of peculiar bones, which, supported upon the 
penultimate vertebral bones and projecting backwards beyond them, 
and seeming to be mere upper spinous processes, or ray bearers, 
unite with the broad inferior spinous processes which have coalesced 
so as to form a vertical fan-like plate. In these, as well as in 
the bony Ganoids mentioned above, the canal for the spinal cord, 
so soon as the vertebrze cease, passes back above the undivided 
‘chorda, and both are invested by a common case of solid cartilage, 
which takes the form of a long cone. It is a further peculiarity of 
the Zeleosted in question, whose caudal rays, with the exception of 
the upper short ones (‘stiitzen strahlen’), are altogether beneath the 
vertebral column, that their terminal vertebra is biconcave. The 
vertebral arches unite in pairs, and form by their proper elongation 
a double spinous process. In one part of these fishes (whose 
ancestors made their appearance in the Jurassic epoch) the arches 
are wedged into pits in the bodies of the vertebra (as in 7Arpssops, 
Tharsts, Leptolepis, Chirocentrites, Elops, Butirinus, Salino, Coregonus, 
Saurus, Sudts, Esox, Umbra). In the others, which only appear 
subsequently in the Chalk, the vertebral arches, and even the roof- 
like bones, are inseparably united with the bodies of the vertebra 
(Clupeide, Cyprinidae, Cobitis). 
“In the great multitude of the remaining 7e/eoste:, the end of 
the vertebral column is far more developed. The chorda is ossified 
to its extreme end, or crystallized into vertebra, the last of which, 
therefore, possesses only a single funnel-shaped cavity, containing 
the end of the chorda, and turned forwards. But in the greater 
number of these Teleostei, whose ancestors made their appearance 
contemporaneously with the second division of the first-mentioned 
roof-tailed fish in the Chalk, the spinal canal alone is prolonged 
behind the last vertebral arches, as a bivalve or tubular bony sheath, 
between the fin-rays. These are the Percide, Scorpenide, Scienide, 
Chromide, Sparida, Squamipennes, Teuthide, Labyrinthiformes, Scom- 
brede, Pecilie, Characine, Mormyride, Silurotdei, and others. The 
smaller number began to exist an epoch later, with the tertiary 
formations, and in these only does the spinal marrow end at the 
same time with the chorda in the last vertebral body, or at least 
in an inseparable process of it (Ladride, Gadide, Blennide, 
T 2 
