THE EXTEENAX STEUCTUEE OP BIEDS. I S3 



These true tail-feathers, or rectrices, have their bases covered 

 and protected both above and below by feathers, vchich take 

 their origin in the trunk, and thence project backvi'ards over 

 the quills and bases of the rectrices. They are generally sraaU 

 and softish feathers (especially those beneath the taU), which 

 tend to complete the conical form of the hinder end of the 

 body. They are called teetrices, i. e. covering feathers or coverts, 

 and those above and below the rectrices are respectively dis- 

 tinguished as the upper and lower tail-coverts. They are 

 always present, but may be very short. The upper ones 

 generally extend less backwards than do the under tall-coverts. 

 They may, however, take on a very great development, as, e. g., 

 in the Peacock, the gorgeous so-called tail of which is not even 

 a true feather-tail, but is formed only of elongated upper tail- 

 coverts (teetrices super iores), which when expanded are held up 

 and supported by the true (though in appearance insignificant) 

 rectrices beneath them. 



"We have now completed our survey of the skin and its 

 appendages — the exoskeleton — of the axial part of the body — 

 the head, trunk, and tail. 



It remains to consider the same system of parts as developed 

 on the two pairs of limbs which constitute the appendicular 

 portion of the bird's bodily frame, being appendages attached 

 to its aocial portion. 



The Limbs. 



We will first consider the anterior pair of Umbs called 

 pectoral, from their situation beside the chest. These " pectoral 

 appendages " are, of course, the wings. 



The Wings. — All birds possess wings, though in some they 

 are very small. Such is the case in the Emeu and the Casso- 

 wary, but above all in the Apteryx. When we speak of the 

 wing of a Bird, we have mainly the feathers of the wing present 

 to our imagination. This is reasonable,- for the feathers are 

 not only the most conspicuous objects, but the direct agents in 

 effecting flight. Nevertheless, the solid structure in which 

 *hey are implanted is of course no less necessary, it forms the 

 basis and solid part of the wing. This solid structure is really 

 the arm of the bird, and its distinct component parts corre- 

 spond with and answer to our own. There is a part which 

 answers to our upper arm and — in all existing birds — a part 



