Miobatrachus romeri;" evidently the inter-centra were paired at about the level of the 16th vertebra, and relatively large.
In these the vertebrae are complete (holospondylous), the centra presumably formed by cylindrical ossification around the notochord, and there is no evidence as to the contributions from embryonic cartilage units.
Neural arches and perichordal centra form in the same manner as in frogs, but with the addition in certain cases (Triton) of a median supradorsal cartilage, which gives rise to the zygapophyses of each neural arch.
The vertebrae, or bony segments of the backbone, generally have their centra hollow on both sides, as in the Ichthyosaurus; but in the neck and tail they are not unfrequently hollow on one side and convex on the other.
The vertebrae have the faces of their centra more or less bi-concave.
The notochord persists between the centra in the dog-fish and rabbit, within the centra in frog.
The centra of the frog are procoelous (hollow in front).
In what important respects do the centra of the vertebrae of the frog, the dog-fish, and the rabbit differ from one another?
The centra of the rabbit have epiphyses, absent in the dogfish and frog.
In Lycoptera of the Jurassic of China the vertebral centra are feebly developed, and the dorsal fin short and posterior.
The symplectic bone is wanting, the notochord is more or less persistent, the vertebral centra always complete constricted cylinders, none coalesced.
In Lepidosteus the spaces between adjacent centra become filled by a secondary development of intervertebral cartilage which then splits in such a way that the definitive vertebrae are opisthocoelous, i.
In the Teleostomes, with the exceptions of those ganoids mentioned, the expanded bases of the arcualia undergo complete fusion to form cartilaginous centra which, unlike the chordacentrous centra, lie outside the primary sheath (figs.
The vertebral centra are opisthocoelous or biconcave, and there are numerous precaudal vertebrae.
The centra of the vertebrae vary enormously, and may be amphicoelous, procoelous, opisthocoelous or flat, but they never have saddle-shaped articulating surfaces.
The first four have centra with saddle-shaped articulating surfaces, but are more or less firmly united together by their neural spines; the last two are completely ankylosed by their centra to the lumbar vertebrae.
The tubercula of the ribs articulate with the sides of the centra of the thoracic vertebrae, not with the transverse processes.
In Labyrinthodontia the centra of the vertebrae are generally well ossified biconcave discs.
The vertebral centra are ossified, and only in exceptionally rare cases have terminal epiphyses.
In the next few vertebrae the centra gradually lengthen, and at the fourth or fifth vertebra the ventri-lateral processes appear and gradually increase in size as followed back.
In some forms however, like Euchirosaurus, the centra are imperfectly ossified, and consist of bony rings traversed by a wide notochordal canal.
The first caudal vertebra of modern Crocodilia is biconvex, and in the Chelonia all types of vertebral centra are found.
In the Ichthyosauria the neural arches were united to the centra by cartilage only.
In Heptanchus the length of the vertebral centra in the middle of the trunk is double that in the anterior and posterior portions, and as the length of the arches does not vary, the long centra carry more of them than do the short centra.
The occipital region of the skull in Amia is clearly formed of three cervical vertebrae whose centra have become absorbed into the cranium, while the neural arches and spines are still distinguishable.
These are eight in number, and are chiefly remarkable for the great variety of articulating surfaces which their centra present, and for their mobility upon one another.
The anterior thoracic vertebrae have short centraand high backwardly-directed neural spines, the lumbar vertebrae have large forwardly-and downwardly-directed transverse processes with expanded ends.
The last cervical is sometimes fused with the succeeding dorsals; the latter are twelve in number, and are fused together so far as concerns their centra and neural processes.
The vertebral centra exhibit distinct epiphyses, which have disappeared in living Sirenians.
It is noteworthy that in Rhytina the cervical vertebrae have the exceedingly thin centra that characterises the neck vertebrae in Whales.
The centra {524} of the vertebrae tend to become ankylosed in old individuals; the caudals have no processes, but are like those quite at the end of the series in long-tailed animals.
The vertebrae of the cervical region are the customary seven, and the centra are thin and plate-like as in the Cetacea, the animal being thus short-necked like those marine creatures.
The cervical vertebrae have short centra as in Hemiganus.
Ossification (Gegenbaur) of the centra appears in a special inner layer of cartilage, which is probably the same as the inner layer of the earlier stage, though this point has not been definitely established.
This sheath forms the basis of the centra of the future vertebrae.
On the twelfth day the ossification of the cartilaginous centra commences.
Defn: The median of the three elements composing the centra of the vertebræ in some fossil batrachians.
Defn: Concave in front; as, procoelian vertebræ, which have the anterior end of the centra concave and the posterior convex.
Defn: Flat at the anterior and concave at the posterior end; -- said of the centra of the vertebræ of some extinct dinouaurs.
Defn: One of the lateral elements in the centra of the vertebræ in some fossil batrachians.
The differences as regards the form of the centra and neural arches die away among the lumbars, and these vertebrae and the caudals are, with a due allowance for greater immaturity, very similar to those of semijunctus.
The centra increase in length posteriorly, the last lumbar having the greatest length of any vertebra in the column.
The anterior zygapophyses and metapophyses maintain a nearly constant position close to the top of the centra throughout the column, from the seventh thoracic backward, and are vertical, thin, and oblong, squared or rounded.
The centra of the thoracic, as well as the lumbar, vertebrae in this individual present inferior median keels, and more or less concave sides, which is not the case in the Barnegat and Newport skeletons.
The centra are very short in proportion to their width.
The neural arches are also noticeably thicker than in semijunctus, and the centra are rounded inferiorly rather than carinated.
Similar but much smaller foramina occur on the sides of the centra of the eighth and ninth caudals.
A curious apparent confirmation of his idea that the centra of the cranial vertebræ are formed from separate halves was supplied in 1839 by Rathke's discovery of the trabeculæ in the embryonic skull of the adder.
These bars, declares Müller, are clearly the still separate halves of the pars basilaris cranii, and represent the divided centra of the two hinder cranial vertebræ.
He found that the vertebral centra were first formed as rings in the chorda-sheath, which give off neural and hæmal processes.
But there is nothing in Rathke's observations to support the idea that the centra of the cranial vertebræ are formed from separate halves.
Flat at the anterior and concave at the posterior end; -- said of the centra of the vertebræ of some extinct dinouaurs.
One of the lateral elements in the centra of the vertebræ in some fossil batrachians.
The centra of the vertebrae retain nearly the same length to the twentieth caudal; but behind this vertebra they are shorter, as are the anterior dorsal vertebrae.
The centra of the dorsal vertebrae, as far as the thirteenth inclusive, have hypapophyses.
The forms of batrachians with which we are acquainted show the vertebral column to have been evolved in the course of time from a notochordal condition with segmented centra similar to that of early bony ganoid fishes (e.
Embolomeri, with the centra and intercentra equally developed disks, of which there are thus two to each neural arch; these disks perforated in the middle for the passage of the notochord.
As a matter of fact, these vertebrae have no centra proper, that part which should correspond with the centrum being formed, as a study of the development has shown (H.
The median of the three elements composing the centra of the vertebr\'91 in some fossil batrachians.
Flat at the anterior and concave at the posterior end; -- said of the centra of the vertebr\'91 of some extinct dinouaurs.
One of the lateral elements in the centra of the vertebr\'91 in some fossil batrachians.
In some instances the centra were pierced in the coronal direction with varying degrees of obliquity; in others the direction was more sagittal; in two of the latter the bullet was retained in the spinal canal.
Fractures of the centra were also frequently only to be assumed from the direction of the wound tracks, and possibly from evidence of nerve injury.
The centra of the anterior vertebrae emit more or less developed descending processes, or haemapophyses, which are sometimes continued throughout (Fig.
Oken supposed that there were four such vertebræ in the skull, the centra being firmly fused and the arches expanded to form the dome of the skull.
These were essentially identical with thecentra of the four vertebræ of Oken.
Later those pads fuse with the anterior end of the centrum of the vertebra to which they belong; where the vertebral column is rendered inflexible, the disks are ossified with the centra and all trace of them is lost.
When the vertebrae are free their centra articulate with each other by complicated joints, exhibiting four types.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "centra" in a variety of sentences. We hope that you will now be able to make sentences using this word.
