Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/736

from the tail. The cervical region of the spine is always long ; and its vertebrae, which are never fewer than eight, and may be as many as twenty-three, are, for the most

part, largo in proportion to those of the rest of the body.

The atlas is a relatively small, ring-like bone ; and the transverse ligament may become ossified and divide its aperture into two an upper for the spinal cord, and a lower for the odontoid process of the axis vertebra. The os odontoideum is always ankylosed with the second vertebra, and constitutes a peg-like odontoid process.

FIG. 2S. A cervical vertebra from the middle of the neck of a Fotrt ; natural

size, a, side view; b, upper view; c, lower view ; pr.z., pre--zygapophyses ; pt.z., post-zygapophyses.

The spines of the succeeding cervical vertebra; are often obsolete, and arc never very prominent in the middle region of the neck. The anterior faces of their elongated vertebral centra are convex from above dowmcards, and concave from side to side ; whilst the posterior faces are cylindrical, slightly excavated from above downwards, and convex from side to side. (The contrary of this is stated in Prof essor Huxley s Verteb. Anim., p. 276, where the author, by a lapsus memoriae, puts it vice versa.) Hence, in vertical section the centra appear opisthoccelons ; in horizontal section, procoelous, and not the contrary, as is stated by our author ; and the structure is exceedingly characteristic of birds. The under surfaces of the centra frequently give off median inferior processes. In the Ratitoe it is obvious that the cervical vertebras have short transverse processes and ribs, disposed very much as in the Crocodilia. For, in young birds, the anterior end of the lateral face of each vertebra bears two small processes, an upper and a lower; and this expanded head of a sty li form rib is articu lated with these by two facets, which represent the capitulum and the tuberculum (Huxley, op. cit., p. 276). In the chicken of the Emeu (Dromceus novcc-hollandice) the writer, in 1843, carefully worked out and figured these parts. Of the twenty cervical vertebrae only the atlas and axis were devoid of distinct ribs ; this individual was six weeks old. These riblets were bony wedges, with a sharp point ; but that was free, and the thick upper end was jammed in between upper and lower transverse processes (diajwphysis and parapophysis). The last but one of the ribs became suddenly larger, and the last was two-thirds the size of its successor the first dorsal. Then followed six large ribs on each side, the last two floating. The vertebra bearing the last of these, and twenty more, are closely embraced by the fore-and-aft growth of the ilium, and form the so-called sacrum, Of the twenty vertebras between the first over lapped bone with a floating rib and the nine ribless caudals, there are five with free ribs, small, and hatchet-shaped, quite like those in the neck of the Crocodile. These, from being attached to a parapophysial cup near the fore-end of the centrum, get more forward, and wedge in between theii own vertebra and the one in front. The next four vertebrae, which give exit to the sacral plexus (or at least to most of it), have no ribs, and are very broad and short. They develop lamellar upper transverse processes, but theii spines are aborted. Then come eleven vertebrae, in front of the free caudal, that have short ribs ; the first two pairs are ankylosed already, then four pairs are distinct, and the remaining five have their ribs ankylosed, and then becoming shorter and more pedate externally, get further backwards on the centrum. Thus, in a Bird as old as six weeks after hatching, there are eighteen pairs of cervi cal, and nine pairs of so-called sacral ribs still distinct. Moreover, the ribs are quite aborted on the first and second cervical, on the four true sacral, perchance, the next after this is also sacral, and on all the caudal vertebrae which have only papilliform transverse processes. There are fifty- five vertebra? in all in the Emeu, thus : cervical, twenty ; dorsal, five ; dorso-lumbar (the first with a large rib and really the sixth dorsal), six; sacral (proper), four; uro- sacral, eleven ; caudal, nine. We shall return to these data in describing the sacrum of the Fowl.

With age the cervical ribs (of the Ratitce) may become completely ankylosed. In Aptcryx australis one, below, remains free ; in Struthio camelus, two ; and in Dromons novce-hollandice, three ; and then they appear like transverse processes, perforated at the base by a canal, which, as in the Crocodilia, contains the vertebral artery and vein, and the main trunk of the sympathetic nerve. The cervical ribs and transverse processes are similarly disposed in very young Carinatce; but in these birds their form frequently becomes much modified in the adult, and they develop prolonga tions which extend downwards and inwards, and protect the carotid artery or arteries. The neural arches have well-developed pre- and post-zygapophyses. The ribs of one or two of the posterior cervical vertebne become elongated and freely movable in the Carinata>, as in the Ratitoe.

The first dorsal vertebra is defined as such by the union of the ribs with the sternum by means of a sternal rib, which not only, as in the Crocodilia, becomes articulated with the vertebral rib, but is converted into complete bone, and is connected by a truo articulation with the margin of the sternum. The number of the dorsal vertebra? (reckon ing under that head all the vertebrae, after the first dorsal, which possess distinct ribs, whether they be fixed or free) varies. The centra of the dorsal vertebrae either possess cylindroidal articular faces, like those of the neck, as is usually the case ; or more or fewer of them may have their faces spheroidal, as in the Penguins [Plovers (and their kin Vanelhts cristatus, Totanusfuscus, &c.), Gulls, Cormorants, and Parrots]. In this case the convex face is anterior, the concave, posterior. They may, or may not, develop .in ferior median processes [which may be simple, as in the Cormorant, where they exist on several lower cervical, on all the dorsal, and in five sacro-lumbar ; or they may bifurcate into two broad, bony leaves, as in Colymbus, They usually possess well-marked spinous processes [which begin in the two or three lower cervicals]. Sometimes they are slightly movable upon one another [bound strongly, in many cases, by ossified tendons of great strength and elasticity]; sometimes they become ankylosed together into a solid mass. [When this takes place the last cervical is ankylosed to the three first dorsal, as in the fowl, the fourth remaining free, and the fifth coalescing with the lumbar; or, as many nsfive may ankylose together, leaving one free, and the last ankylosed to the lumbar, as in Falfo (esalon. But this number often differs with age, as may be seen in different individuals of PsojjJria crepitans, and other, more typical, Cranes.]

It is characteristic of the dorsal vertebrae of Birds that

the posterior, no less than the anterior, vertebrae present a facet or small process on the body, or lov;er part of the arch, of the vertebra for the capitulum of the rib, while the upper part of the neural arch gives off a more elongated process for the tuberculum. Thus, the transverse pro cesses of all the dorsal vertebrae of a Bird resemble those of the two anterior dorsals of a Crocodile, and no part of the vertebral column of a Bird presents transverse pro

cesses with a step for the head of the rib. like those of the