ANATOMY OF THE FOWL 29 



openings one can see through from one nostril to the othei* 

 (nares perviae). The external openings are either round or 

 slit-like. They are often surrounded by a thin dermoid struc- 

 ture and a border of peculiar feathers. Each nostril is pro- 

 vided with a turbinated bone divided into three parts, which 

 may be considered as three turbinated bones. The middle 

 turbinated bone is the largest and the lower one the smallest. 

 A small, flat gland, peculiar to birds (fowls, ducks and 

 geese), lies on the frontal bone in close proximity to the mesial 

 corner of the eye. A duct extends from this gland forward 

 and empties into the nostrils. The posterior nares opens into 

 the mouth cavity through a slit-like opening in the roof of 

 the mouth. 



Larynx 



Air passes through the nostrils and pharynx into the su- 

 perior larynx. The superior larynx is a musculo-cartilaginous 

 valve located at the superior extremity of the trachea. There 

 is no epiglottis. A ring-like cartilage, the cricoid, is located 

 at the base of the larynx. This forms the principal support. 

 This cartilage is divided into four parts, namely, two side 

 parts, one unequal ventral part and an unequal dorsal part. 

 Some of these parts at times and in some species are fused. 

 The arytenoid cartilages, three in number, are flexible and 

 joined to the superior part of the cricoid. These cartilages 

 bound supero-posteriorly the entrance of the larynx. At 

 times the arytenoids become partially bony. 



The walls are smooth and in the superior larynx there 

 are no vocal cords. This organ is sometimes called the larynx 

 cranialis, in contradistinction to the true larynx or larynx 

 caudalis. The true larynx is located at the bifurcation of 

 the trachea into the right and left bronchi; it is provided 

 with delicate vocal cords. This organ is absent in voiceless 

 birds. It is sometimes called the larynx bronchio-trachealis. 

 In fowls it is flattened laterally. The last rings lie close 

 together in fowls, but are connected in pigeons and more or 

 less completely fused in geese. This structure is called the 

 tympanum (drum). A bony, arrow-like passage is found 

 between the tympanum and the opening into the bronchi. 

 This bears a small half-moon-shaped fold, which is concave 

 from above. On either side of this passageway there is lo- 

 cated an elastic membrane, the mebrana tympaniformis in- 

 terna, Avhich forms the inner wall of the adjacent bronchus. 

 Laterally and between the tympanum and the two bronchial 

 rings on either side there is a membrane called the mem- 

 brana tympaniformis externa. Singing birds x)ossess a well 



