176 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



lateral walls of the larynx the two arytenoid cartilages, small cartilages support- 

 ing the two triangular flaps which inclose the glottis between them. Posterior 

 to the glottis is a ring-shaped cartilage, the cricoid, which is much wider on the 

 ventral than on the dorsal side. The arytenoids probably are remnants of the 

 fifth gill arches while the cricoid is the enlarged first cartilage of the series of 

 rings in the trachea. 



Now trace the trachea posteriorly. Note the esophagus, a soft tube, lying 

 dorsal to or to one side of the trachea. Find just anterior to the heart the point 

 where the trachea bifurcates into the two bronchi which proceed to the lungs. 

 Raise the right and left lobes of the liver and the stomach and find dorsal to 

 them against the carapace a large spongy organ, the lung, on each side. Trace 

 a bronchus into each lung; it is accompanied by a pulmonary artery and a 

 pulmonary vein. Study the relation of the lung to the pleuroperitoneal cavity. 

 Note that the lung is in contact with the inner surface of the carapace, and that 

 the parietal peritoneum passes over the ventral surface of the lung leav- 

 ing the lung outside of the membrane. Such a relation to the peritoneum 

 is spoken of as retroperitoneal. The posterior end of the lung, however, 

 projects into the pleuroperitoneal cavity and is clothed with the peritoneum. 

 Cut open the lung and observe its extremely spongy texture; cords of connective 

 tissue divide the interior into air spaces or alveoli. 



The path followed by the air in respiration is : external nares, nasal cavities, 

 internal nares, mouth cavity, pharyngeal cavity, glottis, larynx, trachea, bronchi, 

 and lungs. In the pharyngeal cavity the paths of food and air cross. 



Make drawings to show the parts of the digestive and respiratory systems. 

 Make a diagram of a cross-section through the body at the level of the heart to 

 show the pericardial and pleuroperitoneal cavities and membranes and their 

 relation to the viscera. 



F. THE COELOM, DIGESTIVE, AND RESPIRATORY SYSTEMS OF THE PIGEON 



Obtain a specimen and place in a dissecting pan. The feathers must be 

 removed. It is desirable that the air sacs should have been inflated through the 

 trachea. 



1. The oral cavity and the pharynx. — Open the mouth widely by cutting 

 through the angles of the jaws. An anterior oral cavity and a posterior pharynx 

 are thus revealed. 



a) Oral cavity: Roof and floor of the oral cavity are bounded laterally by 

 horny beaks of epidermal origin which incase the jaws. Teeth are absent, as in 

 all living birds. The roof of the mouth cavity bears a pair of elongated palatal 

 folds with free fimbriated margins. These palatal folds correspond to the hard 

 palate of mammals, but differ in that they do not meet in the median line, 

 leaving here a deep palatal fissure. The hard palate of many birds is therefore 

 a split palate and is normally in the condition which in mammals is the result 



