.XIII PHYLUM CHORD ATA 385 



In the wings and tail certain special arrangements of the feathers 

 are to be distinguished. When the wing is stretched out at right 

 angles to the trunk, twenty-three large feathers (Fig. 1022) are seen 

 to spring from its hinder or post-axial border : these are the 

 remiges or wing-quills. Twelve of them are connected with the 

 ulna and are called cuhitals or secondaries (cb. rmg.). The rest are 

 known as primaries : seven of these are attached to the meta- 

 carpal region, and are hence called metacarpals {mtcio. rmg.), the 

 remaining four or digitals to the phalanges of the second and 

 third digits. These are again distinguished into a single ad- 

 digital {ad. dg. rmx) connected with the single phalanx of the 

 third digit (Fig. 1034, ph.3), two mid-digitals (md. dg. rmg.) with 

 the proximal phalanx of the second digit (Fig. 1034, ph3), and 

 two pre-digitals (pr.dg.rmg.) with its distal phalanx (Fig. 1034, 

 fh.^'), A special tuft of feathers on the anterior border of the 

 wing, arising from the pollex (Fig. 1034, ph.l), forms the ala 

 spuria {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 itpper and under wing-coverts. In the tail there 

 are twelve long rectrices (Fig. 1022, ret.) or tail-quills, springing 

 in a semicircle from the uropygium ; their bases are covered, as 

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

 arrangement is known as the ptcrylosis. 



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 regioji, and the convention is again adopted of 

 counting as the first thoracic (Fig. 1027, th. v. 1), the first vertebra 

 having its ribs united with the sternum. There are fourteen 

 cervical vertebrae, the last or 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 uuiting 

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

 ribs (Fig. 1028, rb.), each having its head fused with the centrum, 

 and its tubercle with the transverse process. The whole rib thus 

 has the appearance of a short, backwardly-directed transverse pro- 

 cess perforated at its base ; the perforation transmits the vertebral 

 artery, and is called the verteirarterial foramen (vrb.f.) 



The centra of the cervical vertebrae differ from those of all other 

 Vertebrata in having saddle-shaped surfaces, the anterior face 

 (Fig. 1028, A) being concave from side to side and convex from 

 above downwards, the posterior face (B) convex from side to side 

 and concave from above downwards. Thus the centrum in sagittal 

 section appears opisthocoelous, in horizontal section procoelous. 

 This peculiar form of vetebra is distinguished as hete7'ocoslous. 



