OSTEOLOGY OF BIRDS 63 



In the nth vertebra the neural spine is more lofty and hooks for- 

 ward ; the spine beneath forms a low median crest nearly as long 

 as the body of the vertebra. The vertebral canals are still increas- 

 ing in caliber. Quite marked changes have gradually come about in 

 the i2tJi vertebra. The neural spine is very pronounced, while the 

 hypapophysis is shrinking again in importance. In the parapophy- 

 ses the form of the diminutive rib begins to be suggested, accom- 

 panied by a corresponcHng enlargement of the vertebral canals. On 

 the centrum, the articular facets are larger, and the anterior one, 

 especially, deeper. The neural canal, still circular, is here larger 

 than we found it in the axis. It seems to have the least caliber in 

 the 6th vertebra. 



In figure 25, the anterior vetebra showni is the 13^^ and it de- 

 parts very markedly from the last one described. Its neural spine 

 now becomes a high quadrate crest nearly as long as the centrum 

 of the bone. 



The transverse processes are heavier, and the bases to the zyga- 

 pophyses very substantial, with little change in the direction of the 

 facets. A rudimentary free rib has made its appearance, the body 

 of which is no longer than its neck. I should have noted a pneu- 

 matic foramen on the lateral aspect of the centrum of the I2'th 

 vertebra; it is still larger here; is seen in the 14th; largest of all in 

 the 15th; very minute in the succeeding one; and disappears in the 

 17th. 



The caliber of the neural canal in the 13th vertebra is circular 

 and large; it gradually diminishes to the 19th, where it is just a 

 little more than half the size. 



The centrum of the 13th vertebra is broader than it is deep, and 

 this segment is quite short from before, backward. Below, a tri- 

 cornute hypapophysis is beginning to be developed. In the 14th 

 vertebra the neural crest is a little longer but no higher; the trans- 

 verse processes are still more spreading. Vhile the free pair of ribs 

 are now quite long, though they do not reach the sternum, or rather 

 are not met by costal ribs. They are devoid of epipleural append- 

 ages. The centrum is evidently becoming narrower and longer, and 

 this contraction and lengthening gradually continues through the 19th 

 or last free vertebra we find before reaching the pelvis, in which the 

 centrum is twice as long as it is wide. The articular facets also in- 

 crease proportionately in size ; the periphery of the posterior articular 

 facets on the centrum of the 19th vertebra is fully double the cir- 



