22 PRACTICAL ORNITHOLOGY. 



Fig. 8 represents the opening of the windpipe into the throat. 

 It is seen to be behind the tongue, «, between the two branches 

 of the hyoid bone, b b, and to present a sUt, c, which is named 

 the rima glottidis, or simply the aperture of the windpipe. 

 This sht-hke opening may be dilated by the action of muscles 

 to be afterwards described, or firmly closed by other muscles ; 

 but in this bird, the Rook, although not in all birds, a triangu- 

 lar vacuity, fZ, is left, which, however, is covered during the 

 act of deglutition by being carried forwards beneath the loose 

 and rugous membrane, e, between it and the tongue. Quad- 

 rupeds have a cartilaginous flap, the epic/lottis, which covers 

 the aperture, but in birds there is no such contrivance. The 

 oval pad, //, in which is the aperture described, has its sur- 

 face composed of mucous membrane, continuous with that of 

 the gullet, and presents several series of small conical papillte, 

 the use of which may possibly be to defend the glottis during 

 deglutition or regurgitation. Before understanding the manner 

 in which the aperture of the windpipe is opened and closed, 

 we must examine the structure of the solid part of the larynx. 



Figs. 4, 5, 6, 7, represent the bones of the larynx : 4 shewing 

 them viewed from before, 5 from behind, 6 from the right side. 

 The form and proportions of these bones vary much in diiferent 

 birds, as we shall afterwards have occasion to see. The largest, 

 marked a in all the figures, is placed in front, and is in this 

 bird of a somewhat ovate form. Being analogous to the thyroid 

 cartilage of the human larynx, it is named the thyroid bone. 

 To the upper and posterior part of the thyroid bone are at- 

 tached, one on each side, two slender curved bones, b i, which 

 are certainly analogous to the cornua of the thyroid cartilage in 

 man, and therefore may be named the appendages of the thyroid 

 hone. Within the nearly complete ring formed by the thyroid 

 bone and its appendages are three other bones, c, d, d\ of which 

 the medial and posterior, c, is all that remains in birds of the 

 cricoid cartilage of the mammalia, which, as its name implies, 

 forms in them a ring of which the anterior part passes below 

 the thyroid cartilage. To this bone, the cricoid, are articu- 

 lated two slender bones, d d, named arytenoid. At their an- 

 terior extremity these bones are attached to the inner surface 



