OSTEOLOGY OF BIRDS 259 



again until we find it as a conspicuous median plate in the 13th. 

 In the 14th it is smaller, and, although still in the vertical plane, 

 evidently moved slightly to the left of the median line. This last 

 condition is more pronounced in the 15th, while in the 16th, where 

 it still possesses considerable size, it is carried so far to the left 

 as to be nearly in the same plane with the side of the vertebra, 

 though it still remains vertical. The 16th vertebra also has lateral 

 hyapophysial cornua, which makes this peculiar shifting of its 

 mid process all the more striking. I am unable to say at present 

 whether this is a constant condition of affairs or not. The dorsal 

 series also have hyapophysial processes ; these are at first short, with 

 spreading cornua, to gradually become longer and lose their termi- 

 nal bifurcation, and again grow shorter, to finally disappear on the 

 first sacral, or dorsolumbar. 



Axis vertebra has a thick and heavy neural spine. In the following 

 six or seven segments this gradually becomes longer, lower, and 

 thinner, to be absent entirely in the 10th cervical vertebra. In the 

 14th it reappears, and from it, backward, it gradually assumes the 

 broad, oblong plate which is perfected in the dorsal series. The 

 vertebrae of this latter region are restricted in their movements 

 upon one another by the many interlacing tendinal and metapophy- 

 sial spiculae among them. 



In the cervical region the neural canal is cylindrical in form, and, 

 owing to the fact that neither the pre- or postzygapophysial facets 

 are upon spreading limbs, in its anterior division this tube is won- 

 derfully well protected, its walls being nearly continuous from one 

 vertebra to the next. This condition does not obtain in the latter 

 half of the cervical region, however, where the prolongation of the 

 aforesaid apophyses lend to the dorsal aspects of the vertebrae, 

 when viewed from above, that familiar capital letter X appearance, 

 with the extremities of the lines alternately articulating above and 

 below. 



This disappears again in the dorsal series, where they are closely 

 interlocked with each other, and the neural tube once more becomes 

 continuous. For the rest we find that the " heterocoelous " plan 

 of articulation prevails among these vertebrae thus far described; 

 that the centra are much compressed laterally in the dorsal region, 

 where also the transverse processes are unusually wide and some 

 of their spiculiform interlacements more than commonly broad. 

 With the exception of the atlas they are all pneumatic. 



