SEC. IV ANATOMY OF BIRDS 205 



it is not jointed, and does not reach the sternum ; while the next 

 to the last cervical has a minute but still free rib (c). In a raven's 

 neck before me, the last cervical rib is about two inches long, 

 articulating by well-defined head and shoulder to body and lateral 

 process of the vertebra ; the penultimate rib is about half an inch 

 long, with one articulation to the lateral process ; while the next 

 anterior vertebra (third from the last) has a minute ossicle, as a free 

 " riblet." The rule is two such free pleurapophyses or cervical ribs 

 of any considerable length : sometimes one ; rarely, three ; in the 

 cassowary four. Eudimentary pleurapophyses may usually be 

 traced up to the second cervical vertebra, as- slender stylets or 

 riblets, completely ankylosed vnth the neural arches in adult life, 

 and lying parallel with the long axes of the bones. The ankylosis 

 of pleuropophyses distinguishes most cervical vertebrae in another 

 way : for from it results, on each side of the neural arch, a foramen 

 (Lat. foramen, a hole, pi. foramina), through which blood-vessels 

 (vertebral artery and vein) pass to and from the skull. The series 

 of these foramina is called the vertebrarterial canal ; none such exist 

 in those posterior cervical vertebrae which bear free ribs ; thus, in 

 the raven the canal begins abruptly at the fourth from the last 

 cervical. But, as in Bhea, for instance (and doubtless in many 

 other cases), the vertebrarterial canal shades visibly into the series 

 of foramina formed by the spaces between the head and shoulder 

 of any rib and the side of the vertebra to which it is attached ; 

 such being the true morphology of the canal. The cervical is the 

 most flexible region of a bird's spine ; the articular ends of the 

 vertebral bodies are the most completely saddle-shaped (hetero- 

 coelous) ; the zygapophyses are large and flaring, overriding each 

 other extensively ; the largest processes are at the fore ends of the 

 bones ; the appositions of the central and zygapophysial articular 

 surfaces are collectively such, that the column tends to bend in an 

 S-shape or sigmoid curve. The vertebral bodies are more or less 

 contracted in the middle, or somewhat hourglass-shaped ; on several 

 lower cervicals hypapophyses are likely to be well developed ; as 

 are neural spines toward both the beginning and end of the series. 

 The vertebrae on the whole are large ; their neural canal is also of 

 ample calibre. The first two cervicals are so peculiarly modified 

 for the articulation of the skull as to have received special names. 



sternal rib." {Anat. Vert. Anim., 1872, p. 237.) Owen appears to regard as dorsal 

 any of tlie vertebrae in question which bear free ribs. The actual uncertainty in the 

 ease, and the discrepant reckoning by diiferent authors, prevents us from making 

 a satisfactory count of the numbers of the two series of vertebrae in any given case. 

 Thus, Fig. 56, as marked by Dr. Shufeldt, shows six dorsals (dv), to which is to be 

 added the one under p, bearing the rib sr ; and from which is to be subtracted the 

 anterior one, bearing the rib c', which is to be regarded as cervical, though its 

 physical characters are evidently those of the dorsal series. 



