xni PHYLUM CHORDATA 373 



angles to the trunk, twenty-three large feathers (Fig. 1033) 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 cubilals or secondaries (cb. rmg.). The rest are known as 

 primaries : seven of these are attached to the metacarpal region, 

 and are hence called metacarpals (mtcp. 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. mix.), con- 

 nected with the single phalanx of the third digit (Fig. 1045, ph. 3), 

 two mid-digitals (md. dg. rmg.) with the proximal phalanx of the 

 second digit (Fig. 1045, ph. 2), and two pre-digitals (pr. dg. rmg.) 

 with its distal phalanx (Fig. 1045, ph. 2'). A special tuft of feathers 

 on the anterior border of the wing, arising from the pollex (Fig. 1045, 

 ph. 1), 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 upper and under wing- 

 coverts. In the tail there are twelve long rectrices (Fig. 1033, 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 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 

 shortness 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. 1038, 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 

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

 vestigial ribs (Fig. 1039, 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 process perforated at its base ; the perforation trans- 

 mits the vertebral artery, and is called the vertebrarterial foramen 

 (vrb.f.). 



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

 Vertebrata in having saddle-shaped surfaces, the anterior face 

 (Fig. 1039, 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 opisthoccelous, in horizontal section proccelous. 

 This peculiar form of vertebra is distinguished as heteroccelous. 

 The centra articulate with one another by synovial capsules, each 

 traversed by a vertical plate of cartilage, the meniscus, with a 



VOL. II A A 



