234 



ANATOMY OF VERTEBRATES. 



in an eminent degree the opposite qualities of strength and light- 

 ness. It terminates below in a more or less obtuse extremity, 

 which is pierced by an orifice termed the loiver umhilicus, fig. Ill, 

 e\ a second orifice, leading into the interior of the quill, is 

 situated at the opposite end, at the point at which the two lateral 

 series of barbs meet and unite ; this is termed the ujiper umbilicus, 

 ih.f. The cavity of the quill contains a series of conical cap- 

 sules fitted one upon the other, and united together by a central 

 pedicle. 



The shaft (scapus) is more or less quadrilateral, and gradually 

 diminishes in size from the upper umbilicus to its distal extremity. 

 It is ahvays slightly bent, and the concave side is divided into two 

 surfaces by a middle longitudinal line continued from the upper um- 

 bilicus; this is the internal 

 ^ ^ - surface, fig. 112, c. The op- 



posite, or external surface, 

 ib. b, is smooth, and slightly 

 rounded ; both sides are 

 covered mth a horny mate- 

 rial similar to that of which 

 the quill is formed, and 

 they inclose a peculiar white 

 soft elastic substance, called 

 the j^ith, ib. a. 



The barbs (rami) are at- 

 tached to the sides of the 

 shaft near the external sur- 

 face, and consist of laminas, 

 varying as to thickness, breadth, and length. They are arranged 

 with their flat sides toward each other, and their margins in the 

 direction of the external and internal sides of the feather ; conse- 

 quently they present a considerable resistance to being bent out 

 of the vane's plane, although readily yielding to any force acting 

 upon themselves in the line of the stem: (e, e, fig. 112, are the 

 bases of two barbs of a feather magnified). The barbules (radii, 

 hamuli), ib. f, f are given off from either side of the thicker 

 margin of the barbs, and are sometimes similarly barbed them- 

 selves, as may be seen in the barbules of the great feathers of the 

 Peacock's tail. In these feathers and in the plumes of the Ostrich, 

 the barbules are long and loose ; but more commonly they are 

 short and close-set, and by their form and disposition constitute 

 the mechanism by which the barbs are united together. The 

 barbules arising from the upper side of the barb, or that next the 



Diagrammatic section of the slaaft aud vane. 



I 



