166 VERTEBRATE ZOOLOGY 



The Mouth and Pharynx. Open the mouth and cut through the 

 angle of the jaw. Carry the cut back through the muscles of the 

 head almost to the opening of the ear. Disarticulate the lower jaw 

 and turn it down, exposing the cavity of the mouth and pharynx. 



There will be seen to be a single space which lies between the 

 edges of the bill and the oesophagus, that part of it within the 

 bill being the mouth cavity, and the posterior part the pharynx. 

 This latter space is where the course of the respiratory air from 

 the nostrils to the lungs crosses that of the food from the mouth 

 to the stomach. 



Note the long tongue and its shape. Just back of it is the 

 glottis, the opening into the larynx and the windpipe; note its 

 shape and the character of its lips. Back of the glottis is a paired 

 transverse membrane with fringed edges, projecting from the floor 

 of the pharynx; behind it is the opening of the oesophagus. 

 Note the two elongated plates which form the roof of the mouth ; 

 also the serrated medial edges of their hinder portion. Note the 

 elongated, paired internal nares, through which the nasal capsules 

 open into the pharynx ; they are in the roof of the pharynx, oppo- 

 site the glottis. Just behind them is the single median opening of 

 the paired Eustachian passages, which join the pharynx with the 

 tympanic cavity ; pass a bristle through it. Note the paired folds 

 in the roof of the pharynx opposite the fringed ventral folds, all 

 of which guard the opening into the oesophagus. 



Exercise 4. Draw a sketch of these structures on a scale of 2. 



The Internal Organs ; the Air Sacs. These sacs arise from the 

 outer surface of the lungs and extend as thin-walled pockets among 

 the viscera and the muscles, and beneath the skin ; they extend also 

 into many of the bones, such as the humerus, femur, and sternum. 

 A branch of a bronchus leads directly to each sac. 



Insert a blowpipe into the glottis and inflate the lungs and the 

 air sacs. 



There are several important sacs. The paired abdominal sacs lie 

 near the dorsal wall of the abdominal cavity, dorsal to the intes- 

 tine, coming near the ventral surface posteriorly; they join the 

 hinder end of the lungs. The paired posterior thoracic sacs lie 



