THE ANATOMY OF BIHD.S. — OSTEOLOGY. 139 



Ntylutis or riblets, completely auchyLjsod with the neural arches in ailult life, aud lying parallel 

 with the long axes of the boues. Tlie anchylosis of pleuropophyses distinguishes most cervical 

 Yertehrte in another way: for from it results, on each side of tlie neural arch, a foramen 

 (Lat. foramen, a Inde, i>l. fo rami na), through which bLjod- vessels (vertebral artery and vein) 

 pass to aud from the skull. The s<'ries of these fii-andna is called the vertehrarterial ca}ial : 

 none such exist in those jjostcrior cervi(tal vertebraj which bear free ribs ; thus, in the raven the 

 canal begins abruptly at the fourth from the last cervical. But, as in Eliea for instance (and 

 doubtless in many other cases), the vertebrarterial canal shades visibly into the series of 

 foranuna firmed by the spaces between the bead and shoulder of any rib aud tbe side of the 

 vertebra to whicli it is attached ; such being, as 1 suppose, the true morphology of the canal. 

 The cervical is the most flexible region of a bird's s(iine ; the articular ends of the vertebral bodies 

 are the most completely saddle-shaped (heterocoelous) ; the zygapiiphyses are large and flaring, 

 overriding each other extensively ; the largest pn icesses are at the fore ends of the bones ; the ap- 

 positions of the central and zygapophysial artbmlar surfaces are c(jllectively such, that the ccdunm 

 tends to bend in an S-shape or sigmoid curve. Tlie vertebral bodies are mcjrc or less C(jntracted 

 in the middle, or somewhat hour-glass-shaped ; on several lower cervicals, bypapophyses are 

 likely to be well developed ; as are neural .spines toward both the beginning and end of the 

 series. The vertebrte on the whole ai-e large ; their neural canal is also of ample calibre. Th(! 

 first two cervicals are so peculiarly modified for the articulation of the skuU as to have received 

 special names. The firat one, tig. .56, at, the atlas (so called because it bears up the head, as 

 the giant Atlas was fabled to supi)ort the firmament), is a simple ring, apparently without a 

 centrum. Tbe lower part of the ring is deeply eui)ped to receive tbe cimdyle of the occiput 

 into ball-and-socket joint. The second cervical is the axis, ax, whicdi subserves rotary move- 

 ments of the skull. It has a peculiar tooth-like odontoid (Gr. ihovs, oSoVror, odous, odontos, 

 tooth ; elhos, eidos, form) process, borne upon the anterior end of its body, fitting into the lower 

 part of the atlantal ring ; about which juvot the atlas, bearing tlie head, revolves like a wheel 

 upon an eccentric axis. The cervicals of birds vary greatly in number; according to Huxley 

 there are never fewer than eight, aud there may be as many as twenty-three; Stejneger gives 

 t\ieiity-fouv for some of the swans. Twelve to fourteen may be about an average number. 



Thoracic or Dorsal Vertebrte (fig. 56, dr) extend from the cervical to or into tin- 

 pelvic region of the spine. In most animals, and in ordinary anatomical language, a "dorsal" 

 is one which bears a distinct free rib, and is therefore truly thoracic, since "ribs" are tbe side- 

 walls of the chest. But in Ijirds, as we have seen, certain cervicals have distinct elongate 

 ribs; and, as wiU be seen soon, long jointed pleurapophyses are usually found in that region 

 commonly called "sacral." The first dorsal, in birds, is arbitrarily considered to be that one 

 which bears tbe first rib which is jointed, and which readies the sternum by its lower (bEema- 

 ]>opbysial) half. Five or six vertebra; of bu-ds commonly answer this description ; though the 

 last one which bears a long free jointed rib (which may or may not reach the sternum) is com- 

 monly auebylosed with the sacrum, as sr. So few as only three ha;mapophysis-bearing ribs may 

 reach the sternum. There may also be a long free-jointed rib which " floats" at both ends; 

 4. e., is articulated neither with tlie sternum nor with the vertebra to which it belongs as in the 

 loon, for example. As the dorsal series thus shades insensibly behind into another series, the 

 lumbar (which has no free, nor any cZt.s^mci ribs, — ribs that one would not hesitate to call 

 such), it is best to consider as dorsal or thoracic all those vertebra;, succeeding the last 

 cervical (which is to be determined as explained in the last paragraph), which have distinct 

 jointed ribs, whatever the connection or disconnection of such pleurapophyses at either end. 

 On this understanding, one, sometimes two or even three " dorsal " vertebra anchylose with 

 the pelvic region of the spine. Fixity of the dorsal region being of advantage to flight, these 

 vertebra are very tightly locked together; not only by tbe close apposition or even 



