518 REPORT OF NATIONAL MUSEUM, 1888, 



The vertebrsB diifer considerably amoug themselves in size, but for 

 reasons already given it is impossible to determine the amount of varia- 

 tion in the vertebral column taken in its entirety. 



The odontoid notch of the atlas presents great diversity of shape, ap- 

 pearing in two cases as a mere slit, while in three out of fifteen speci- 

 mens ossification has bridged over the notch and converted it into a 

 foramen so that the atlas presents very much the appearance of having 

 belonged to one of the higher altrices. , 



The shape and size of the neural canal varies, but it is always wider 

 than high. The centrum of the axis is subject to much variation in 

 size and shape, and the various processes are equally diversified. In 

 very rare instances the vertebral artery sends a branch upward through 

 a minute foramen at the base of the metapophysis, but ordinarily there 

 is only a notch present at this spot. The sixth to ninth cervicals, in- 

 clusive, have many features in common and these resemblances render 

 it extremely difficult to distinguish them from one another when, as in 

 the present instance, a large number are mixed together, since, for ex- 

 ample, the sixth vertebra of a large bird is almost the exact counterpart 

 of the seventh of a smaller specimen. In fact, but for Professor Owen's 

 memoir on the Great Auk, the " making up " of skeletons would have 

 been extremely difficult owing to the amount of individual variation. 



The tenth cervical, however, was shown by Professor Owen's paper 

 to have a very characteristic shape, being distinguished by a broad 

 hypapophysis directed forward, and this furnished one point of depart- 

 ure for the arrangement of the vertebral column. 



In the dorsal region there are differences in the development of the 

 hypapophyses, but these seem as might be supposed, to be correlated 

 with differences in the size and strength of individuals. 



The length, strength, and curvature of dorsal and sternal ribs is of 

 course variable, and the number of epipleural appendages seems to have 

 been by no means constant. 



It may be said that comparatively few epipleurals could be found, as 

 these little bones are so thin that they readily decompose. 



The skeleton described by Professor Owen seems to have been that 

 of a very old bird, and epipleurals were present on the second pair of 

 cervical ribs, this, in the light of the material in hand, being of ex- 

 tremely rare occurrence. 



A most interesting and instructive variation is of frequent occurrence 

 in the " sacrum " which is composed of fourteen vertebrae, the first bear- 

 ing the eighth, and ordinarily the last, pair of ribs. But it often hap- 

 pens that the second sacral also shows articulations, indicating the 

 presence of a ninth pair of ribs, and it is interesting to note that when 

 this extra pair of ribs is present there is usually found to be a rudimen- 

 tary pair of parapophyses developed on the first true sacral, as if the 

 rib creating force had been felt still further down the line of vertebroe. 



Twenty-three out of one hundred and forty-four sacra had an extr^, 



