5o8 MANUAL OF ZOOLOGY SEC. 



the pharynx, with which it communicates through a slit-like 

 aperture. It contains the vocal cords. Leading backwards 

 from the larynx is the trachea or windpipe (//".), a long tube 

 the wall of which is supported by cartilaginous rings which 

 are incomplete dorsally. The trachea enters the cavity of 

 the thorax and there divides into the two bronchi, one 

 passing to the root of each lung. 



The lungs are enclosed in the lateral parts of the cavity 

 of the thorax. Each lung lies in a cavity lined' by a 

 membrane the cavity of the pleural sac or pleural mem- 

 brane. The right and left pleural sacs are separated by 

 a considerable interval owing to the development in the 

 partition between them of a space, the mediastinum, in 

 which lie the heart and other organs. The lung is attached 

 only at its root where the pleural membrane is reflected 

 over it. In this respect it differs widely from the lung of 

 the bird. It differs also in its minute structure. The 

 bronchus entering at the root divides and subdivides to 

 form a ramifying system of tubes each of the ultimate 

 branches of which, or terminal bronchioles, opens into a 

 minute chamber or infundibulum, consisting of a central 

 passage and a number of thin-walled air-vesicles or alveoli 

 given off from it. 



The spleen is an elongated, compressed, dark red body 

 situated in the abdominal cavity in close contact with the 

 stomach, to which it is bound by a fold of the peritoneum. 

 The thymus, much larger in the young Rabbit than in the 

 adult, is a soft mass, resembling fat in appearance, situated 

 in the ventral division of the mediastinal space below the 

 base of the heart. The thyroid is a small brownish, bilobed 

 glandular body situated in close contact with the ventral 

 surface of the larynx. 



The neural cavity contains the central organs of the 



