2IO ZOOTOMY. 



beak, devoid of feathers but covered with a strong, horny 

 sheath, except at the base, where there is on each side a 

 tumid naked area of skin, the cere. 



125. The mouth, bounded above and below by the 

 upper and lower divisions of the beak (upper and lower 

 mandibles of ornithologists). 



126. The nostrils, or external nares, oblique, slit- 

 like, paired apertures immediately in front of the cere. 



127. The eyes, situated a little posterior to the angle of 

 the mouth : each is provided with an upper and a lower 

 eyelid, both devoid of feathers, and with a nictitating 

 membrane, which is easily found in the anterior angle 

 of the eye, and can be pulled backwards over the eye as a 

 whitish, semi-transparent membrane. 



128. The auditory aperture, situated a short distance 

 below and behind the eye, of a rounded form, and lead- 

 ing into a canal, the external auditory meatus : in the 

 entire bird the auditory aperture is quite concealed by the 

 feathers. 



129. The flaccid condition of the skin about the neck, 

 due to the more or less empty condition of the crop 



(§ 15°)- 



130. The breast of the bird, formed by the muscles 

 covering the sternum : the keel of the latter (§ 87) can be 

 felt as a median bony ridge extending from a short distance 

 behind the root of the neck to within i^ inches of the 

 posterior extremity of the body. 



131. The soft, ventral, abdominal walls behind the 

 posterior edge of the sternum, bounded externally and 

 posteriorly by the pubes (§ 105). 



132. The vent, or cloacal aperture, a considerable 

 transverse cleft with tumid lips, situated on the ventral 

 surface of the hinder end of the trunk. 



