STRUCTURE OF APPENDAGES 311 



These barbules hook together the barbs and give the web its form. 

 In some feathers, as the hackle, and in the wing bar feathers of the 

 male of some breeds, there is a portion of the upper outer edge of the 

 feather not provided with barbules, "which fact gives the feather its 

 characteristic appearance. The down feathers are loose and fluffy. 

 In this kind of feather the shaft is weak, and the barbs are not 

 provided with barbules. The barbs like the shaft may be considered 

 weak. These feathers give great warmth to the body. There are 

 fiber feathers appearing as hair-like filaments, and called filo-pluma. 

 These are found scattered over the body; they are particularly abun- 

 dant in the region of the head and the neck. 



At each end of the quill is a small opening, or umbilicus. Inside 

 the barrel of the feather there is pulp, which in young feathers is 

 very vascular; the vessels entering by the proximal umbilicus are 

 buried, along with part of the quill, in a papillated follicle of the 

 skin. From this follicle the feather is developed. At the base of 

 the shaft a secondary rudimentary quill is usually formed, which 

 may be represented by a mere tuft of down. On the same general 

 principle the smaller feathers are constructed. These cover the 

 body, the upper parts of the legs, and the head, while the larger 

 feathers and quills are confined to the wings and the tail. The 

 longest quill feathers are those arising from the hand, called the 

 primaries. Those arising from the forearm are called the second- 

 aries. Those that are developed from the proximal part of the arm 

 are called the tertiaries. The rudimentary pollux carries some feath- 

 ers which form the alula, or bastard wing. The scapularies are 

 feathers covering the scapula and the humerus. Covering the 

 bases of the larger flight feathers are wing coverts consisting of 

 several rows of small feathers. The quill feathers of the tail are 

 called the rectrices. The rectrices have considerable mobility; their 

 bases are covered by a row of tail coverts. 



The pedal digits of the natatores are joined by a membrane, 

 covered with scaly skin, which forms the web foot. 



The feathers in many parts of the body are developed in rows, 

 there being intervals, or elongated skin areas, between these groups 

 of several rows, which are not provided with feather papillae, but 

 which are covered over by the feathers developed in front of these 

 spaces. The definite feather lines, or areas, have been called 

 pteryla. The intervening tracts devoid of feathers are called the 

 apteria. 



