XIII 



PHYLUM CHORDATA 



357 



the proximal phalanx of the second digit (Fig. 975,j0#), and 

 two pre-digitals (pr.dg.rmg.) with its distal phalanx (Fig. 975, 

 pli.2'}. A special tuft of feathers on the anterior border of the 

 wing, arising from the pollex (Fig. 975, ph.l), forms the ala 

 spnria (al. sp.). The spaces which would otherwise be left between 

 the bases of the remiges are filled in, both above and below, by 

 several rows of upper and under wing-coverts. In the tail there 

 are twelve long rectrices (ret.) or tail-quills, springing in a semi- 

 circle from the uropygium ; their bases are covered, as in the 



c.pt 



cd.ipl: 



FIG. 967. Pterylosis of Columba livia. A, ventral ; B, dorsal, al. pt. alar pteryla or wing- 

 tract ; c. pt. cephalic pteryla or head-tract ; cd. pt. caudal pteryla or tail-tract ; cr. pt. crural 

 pteryla; cr. apt. cervical apterium or neck-space ;///(. pt. femoral pteryla; hv.. pt. humeral 

 pteryla ; lot. apt. lateral apterium ; sp. pt. spinal pteryla ; v. apt. ventral apterium ; v. pt. 

 ventral pteryla. (After Kitsch.) 



wing, by upper and under tail-coverts. The whole feather-arrange- 

 ment is known as the pterylosis. 



Endoskeleton. The vertebral column is distinguished from 

 that of most other Craniata by the great length and extreme 

 mobility of the neck, the rigidity of the trunk-region, and the short- 

 ness of the tail. As in Reptilia, the cervical passes almost insensibly 

 into the thoracic region, and the convention is again adopted of 

 counting as the first thoracic (Fig. 968, th. v. 1), the first vertebra 

 having its ribs united with the sternum. There are fourteen 

 cervical vertebras, the last two of which have double-headed ribs 

 (cv.r.) each having its proximal end divisible into the head proper 

 articulating with the centrum of the vertebra, and a tubercle with 

 the transverse process : their distal ends are free, not uniting 

 with the sternum. In the third to the twelfth there are vestigial 



