368 



HISTOLOGY 



FIG. 332. Very early rudiment of a down feather in a pigeon. 

 />., papilla; ep., epidermis. (After DAVIES.) 



found, and not so pronounced a thickening of the mesodermal rudiment 



of the papillae as is to be seen in the feather anlage. 



The feather is very complicated in its development, and we shall 



describe the com- 

 pleted structure first 



( Fi g- 333)- It con- 

 sists of a more or 

 less long quill which 

 is set in a follicle 

 much as a hair is. 

 The quill is a hollow 

 tube in which is usu- 

 ally found a loose parchment-like series of irregular lamellae which 

 divide it into several chambers. At its proximal extremity, in the bot- 

 tom of the follicle, it opens through a slightly constricted neck, and a 

 mass of vascular mesodermal pulp, covered with the stratified epithe- 

 lium of the follicle, reaches up for a distance into its lumen. This 

 structure is the feather papilla, and the 

 opening is known as the interior umbilicus. 

 The quill rests against the sides of the fol- 

 licle which are covered with the invagi- 

 nated stratified epithelium. Distally, the 

 short quill is extended into a longer and 

 somewhat smaller shaft known as the rachis. 

 At the point of juncture there is another 

 small opening, the superior umbilicus. 



The rachis has a solid wall with an alve- 

 olar core, and from each of its two sides 

 springs a longitudinal row of more closely 

 set, parallel, thin plates called the barbs. 

 Projecting again from the upper or distal 

 edge of each barb are two rows of very 

 small processes known as the barbules. 

 The anterior row of barbules is provided on 

 its lower side with a series of tiny hooks, 

 while the posterior row is shaped into a 

 series of tiny, ragged-edged plates so placed 

 that the anterior barbules of the next barb 

 will catch in them and hold as strongly as 

 their elasticity will permit. When forced 

 apart, the hooks, if uninjured, will catch 

 again the next time they touch the plates of the neighboring barbule. 

 All these structures, the quill, rachis, barbs, and barbules are dead 



FlG. 333. Lower portion of a 

 nearly completed down feather in 

 the pigeon, q., quill; cy.c., cyl- 

 inder cell layer; d.f., beginning 

 of the growth of the definitive 

 feather. (After DAVIES.) 



