Vertebrce of Fowl. 87 



two vertebrae co-ossified with the occipital bone in the higher 

 vertebrate, which must, therefore, be looked upon as the 

 equivalents of the two first vertebrse of the frog, whose atlas, in 

 consequence, is not to be strictly compared with the atlas of 

 either bird or mammal. 



The vertebral chain of the Fowl has been found to consist 

 of 46 or 47 vertebrae. The number appears to be rather 

 less than this ; but it will be noted that the posterior end of 

 the column is formed of a ploughshare-shaped bone, the 

 pygostyle or urostyle, which is really a compound bone made 

 up of separate elements. These separate vertebrae can be 

 divided into four series. There are, first of all, the cervical 

 vertebrcB, sixteen in number. The term "cervical " is commonly 

 applied to those in front of the first vertebra, which bears 

 a complete rib articulating with the sternum ; but really there 

 is no hard-and-fast line of division, since the last two of the 

 cervical series bear free ribs, which, although they do not 

 reach the sternum, increase progressively in length. The 

 cervical vertebrae lying in front of these latter appear to have 

 no ribs; but they really have short ribs, which are firmly 

 coalesced with the vertebra, so as to surround a canal, through 

 which an artery passes. Each cervical vertebra, like the 

 remaining vertebrae, except those at the tail end of the body, 

 consists of a centrum, which articulates in front and behind 

 with the preceding and succeeding vertebra by a surface which 

 is concave in the middle, and more convex peripherally ; it has 

 been compared to the outline of a saddle, and the centra of 

 birds have been described as having saddle-shaped articulating 

 surfaces. This method of articulation ensures considerable 

 mobility, and the neck is long. Rising from the centrum is an 

 arch of bone, tlie neural arch, which projects at the top in 

 a varying degree to form the mural spine ; this surrounds the 

 large neural canal, in which lies the spinal cord. The ribs are 

 attached by two heads : by a capiUihtm to a smooth surface 

 upon the centrum, and by a tuberculum to an outgrowth of 

 the neural arch, the transverse process. In addition to these 

 various processes and regions of the vertebra, there is 

 commonly a ventral median process, the hypapophysis, which 



