Vertebra

“ In the Hauts-vertébrés the vertebræ are internal; in the Dermo-vertébrés they are external. "Every animal lives either outside or inside its vertebral column." [91] The essence of a vertebra is not its form, nor its function, but its composition from four 061elementary pieces which unite round a central space (Isis, loc. cit., p. 532) . Serres had shown that in the higher animals every vertebra is formed from four centres of ossification, that the body of the vertebra is at first tubular, and that afterwards it becomes filled up. ”

“ The principal mass of bone in each vertebra is the body, or centrum, which is typically a cylinder, or modification of that form, and the two ends of the cylinder are the faces, by which the successive vertebræ are in contact with one another. ”

“ The form of the extremities of the body of the vertebræ, especially of the posterior, is sub-hexagonal, the breadth being to the depth as eight to five. The sides and under part of the vertebræ are slightly concave; on the inferior surface there are two ridges, continued forwards from the posterior margin of the vertebra, each situated about an inch distant from the middle line; they converge as they pass forwards, and are gradually lost in the level of the vertebra; their greatest elevation does not exceed half an inch. ”

“ In all the higher non-degraded vertebrata we find a certain uniform type of skeleton, consisting of the head, the vertebral column, and four limbs; and these last, in the various symmetrical forms, whether exemplified in the higher fish, the higher reptiles, the higher birds, the higher mammals, or in man himself, occur always in a certain determinate order. In all the mammals, the scapular bases of the fore limbs begin opposite the eighth vertebra from the skull backwards, the seven which go before being cervical or neck vertebræ ”

“ These cranial vertebræ, four in number, correspond, it is said, to the four senses that have their seat in the head: there is the nasal vertebra, the centrum of which is the vomer, its spinal processes the nasal and ethmoid bones, and its ribs the upper jaws; there is the ocular vertebra, the centrum of which is the anterior portion of the sphenoid bone, its spinal processes the frontals, and its ribs the under jaws ”

“ And if we trace up the development of the vertebral column from its primitive form of a cartilaginous cord in the lowest fishes, we see that, throughout, it maintains an integration corresponding to the unity of the incident forces, joined with a division into segments corresponding to the variety of the incident forces. Each segment, considered apart, exemplifies the truth more simply. A vertebra is not a single bone, but consists of a central mass with sundry appendages or processes ”

“ A typical vertebra consists of a centrum, and an arch, with articular surfaces for two ribs, and is called heterocoelous when the facets, or connecting surfaces, are saddle-shaped, a condition characteristic of, and restricted to, Birds. ”

“ In the many familiar cases of the abbreviation or elongation of the vertebral column in adaptation to certain habits, a vertebra in the middle of a series can not dwindle out of existence, it must suddenly drop out or suddenly appear. ”

“ Cut the flesh from the thick portion of the tail.
8. Cut off the head at the first cervical vertebra, and clean the skull as previously described elsewhere, but leave the hyoid bone in its place.
9. Cut the flesh away from the neck vertebræ as well as you can. Be careful not to cut the sternum (or breastbone) , which is soft cartilage, and easily cut; nor the ends of any vertebral processes, nor any soft bones.
10. If the skeleton is a small one, it is apt to get quite bloody during the operation. ”

“ In the wide range of the animal kingdom there are scarce any two pieces of organization that less resemble one another in form than the vertebræ of the placoids resemble their skulls; and the difference is not merely external, but extends to even their internal construction. In both skull and vertebræ we detect an union of bone and cartilage; but the bone of each vertebra forms an internal continuous nucleus, round which the cartilage is arranged, whereas in the skulls it is the cartilage that is internal, and the bone is spread in granular points over it. ”

“ The surface is smooth, regularly convex from side to side, and gently concave from back to front. The last vertebra shows the articular vertebral surface; it is convex in both directions, and oblique, so that a large part looks upward. ”

“ Fig. 13. 1. The cartilaginous substance which connects the bodies of the vertebræ. 2. The body of the vertebra. 3. The spinous process. 4,4. The transverse processes. 5,5. The articular processes. 6,6. A portion of the bony bridge which assists in forming the spinal canal (7) .
Fig. 14. Backbone, spinal column, or vertebral column. All animals possessing such a row of bones are called vertebrates. Above b are the cervical (neck) vertebræ; b to c, dorsal (back) or chest vertebræ; c to d, lumbar (loins) vertebræ ”

“ Apply this spinal branch of phrenology to the Sperm Whale. His cranial cavity is continuous with the first neck-vertebra; and in that vertebra the bottom of the spinal canal will measure ten inches across, being eight in height, and of a triangular figure with the base downwards. As it passes through the remaining vertebrae the canal tapers in size, but for a considerable distance remains of large capacity. Now, of course, this canal is filled with much the same strangely fibrous substance—the spinal cord—as the brain; and directly communicates with the brain. ”

“ All along the spinal column, and between each two adjoining bones, are openings on each side, through which nerves pass out to be distributed to various parts of the body.
Between the vertebræ are pads or cushions of cartilage. These act as “buffers,” and serve to give the spine strength and elasticity and to prevent friction of one bone on another. Each vertebra consists of a body, the solid central portion, and a number of projections called processes. ”

“ In the animal, nature makes a vertebra, or a spine of vertebrae, and helps herself still by a new spine, with a limited power of modifying its form,—spine on spine, to the end of the world. A poetic anatomist, in our own day, teaches that a snake, being a horizontal line, and man, being an erect line, constitute a right angle ”

“ Most of the ribs have a head divided by a little ridge into two facets for articulation with the dorsal vertebræ, a flattened neck, a tuberosity at the base of the neck with a facet for articulation with the transverse process of the vertebra below, an angle, and a shaft, which is externally convex and is grooved on its lower edge for the intercostal vessels and nerve. ”

“ THE VERTEBRAE
The spinal column or backbone of reptiles, as of all other air-breathing vertebrates, is made up of a variable number of separate segments called vertebrae. A vertebra (Fig. 73 b) is composed of a body, or centrum, and an arch, or neurapophysis, each ossifying separately and uniting at variable times, the neurocentral sutures more persistent than in most mammals, young or aquatic reptiles always (Fig. 87 b, c) , adult land reptiles often showing them. [1] ”

“ Taking the dorso-lumbars, or trunk-vertebræ, as a single series, we may note that in a few mammals (e.g. the elephants) all the neural spines have a backward slope, but in the great majority of forms this backward inclination ceases near the hinder end of the dorsal region, where there is one vertebra with erect spine, while behind this point the spines slope forward.
Fig. 15.—Third lumbar vertebra of Wolf, front end and left side. tr., transverse process. cn., centrum. pr.z. and pt.z., anterior and posterior zygapophyses. n.sp., neural spine. ”

“ The theory of the skull which held the field was known as the vertebral theory. The great bulk of the nervous system of vertebrate animals consists of a mass of tissue lying along the dorsal line of the body and enclosed in a cartilaginous or bony sheath. The nerve tissue is the brain and spinal cord; the sheath is the skull in front and the vertebral column along the greater part of the length of the animal. ”

“ Make a man lean forwards, with his arms folded across the chest; this will make prominent the spines of the vertebræ. The lower border of the trapezius will guide you to the spine of the twelfth dorsal vertebra. ”

“ Cervical vertebrae, or those between the skull and the first vertebra which is connected with the sternum by a pair of complete ribs. The last 1 to 5 of these vertebrae have movable ribs which do not reach the sternum, and are called cervico-dorsals. (2) Dorsals, those which begin with the first thoracic rib, and end at the last that is not fused with the ilium. The term “lumbar” vertebrae is inapplicable to birds. (3) Pelvic, all those which are fused with the iliac portion of the pelvis, generally a considerable number. (4) Caudal, those which are not connected with the pelvis. ”

“ If pectoral and abdominal muscles are repeated in the face, so also must the anterior bones, ribs, and limbs be repeated. It will be shown, in treating of the organs, that the nose is a vertebra, the jaws members, and their muscles those of the limbs. The head is the whole trunk with all its systems. The brain is the spinal365 marrow, the skull the vertebral column, the mouth intestine and abdomen, the nose lung and thorax, the jaws are members. ”

“ The Spine, Spinal or Vertebral Column, chine or backbone in man consists of a number of superimposed bones which are named vertebrae, because they can move or turn somewhat on Spine
each other. It lies in the middle of the back of the neck and trunk; has the cranium at its summit; the ribs at its sides, which in their turn support the upper limbs ; whilst the pelvis, with the lower limbs, is jointed to its lower end. ”

“ It is held by a class of naturalists, some of them of the highest standing, that the skulls of the vertebrata consist, like the columns to which they are attached, of vertebral joints, composed each, in the more typical forms of head, as they are in the trunk, of five parts or elements,—the centrum or body, the two spinous processes which enclose the spinal cord, and the two ribs. ”

“ But, after all, it is not of the essence of the vertebrate type to have the trunk and the abdomen attached at definite and invariable distances along the vertebral column—that is a notion surviving from the anatomy which made man its type. ”

“ Whether certain bones in one vertebrate animal’s skeleton correspond with certain bones in another’s, or in every other’s, is one question; and whether the skeleton of every vertebrate animal is divisible into a series of segments, each of which is modelled after the same type, is another question. ”

“ A peculiar fact may here be noticed with reference to the formation of the vertebral bodies in the tail of Scyllium, Raja, and possibly other forms, viz. that there are double as many vertebral bodies as there are myotomes and spinal nerves. This is not due to a secondary segmentation of the vertebræ but, as I have satisfied myself by a study of the development, takes place when the vertebral bodies first become differentiated. ”

“ Every anatomist, in order to comprehend the physiology and anatomy of this class, begins his analysis of the vertebrate skeleton by observing two distinct systems of organization—the dermal and the neurohæmal, heretofore supposed to be peculiar to vertebrates. Now, to which system, the dermal or the neurohæmal, do the extremities belong? No amount of ingenuity can satisfy the thoughtful student that the limbs are evolutions of the appendages of the neurohæmal axis. They are dermal. Even in mammalia they have no proper union, no true articulation with the spinal column. ”

“ By the vertical movements of the sixth and succeeding trunk vertebrae, with the interspinous bones which they support, on the rigid structure formed by the head and first five vertebrae, the file-like first interspinous bone moves backwards and forwards, and, by scraping against the ridges on the inner surfaces of the cleft neural spines, gives rise to a harsh grating noise, which is particularly unpleasant when artificially produced. ”

“ Every Vertebrate has a backbone; every Vertebrate has a bony arch above that backbone and a bony arch below it, forming two cavities,—no matter whether these arches be of hard bone, or of cartilage, or even of a softer substance; every Vertebrate has the brain, the spinal marrow or spinal cord, and the organs of the senses in the upper cavity, and the organs of digestion, respiration, circulation, and reproduction in the lower one ”

“ That which is true of the limbs, is also true of all the organs; and it is on this ground that we speak of the vertebrate type. From fish to man one common plan of structure prevails; and the presence of a backbone is the index by which to recognize this plan. ”

“ All we know of the origin of limbs shows that they commence as outgrowths upon the surface of the body, and that the first-formed portions are the most distal segments. The limb, as proved by its permanent state in the lowest vertebrates, and by its embryological condition in higher forms, is at first a mere projection or outward fold of the skin, which, in the course of development, as it becomes of use in moving or supporting the animal, acquires the internal framework which strengthens it and perfects its functions. ”

“ We now come to Bone, a tissue confined to the vertebrata, and typically shown only in the higher types. As we descend in the scale from birds and mammals to lizards, amphibia (frogs and toads) and fish, we find cartilage continually more important, and the bony constituent of the skeleton correspondingly less so. In such a type as the dog-fish, the skeleton is entirely cartilaginous, bone only occurs in connection with the animal's scales; it must have been in connection with scales that bone first appeared in the vertebrate sub-kingdom. ”