172 



ELEMENTS OF MAMMALIAN ANATOMY. 



ing the same in a drop of saliva on a glass slip, which 

 is then to be examined with a microscope magnifying 

 about 300 diameters. The diaphragm of the microscope 

 should be arranged so as to admit but little light. 



The lungs together with the heart fill up the greater 

 part of the thoracic cavity. In a cat recently killed the 

 lungs may be expanded by tying a piece of glass tubing 

 on the trachea and blowing into it strongly for a few 

 seconds. Each lung is completely invested by a sac of 



delicate transparent serous mem- 

 brane called pleura (Fig. 80). 

 Each sac is reflected at the root 

 of the lung, where the blood- 

 vessels and bronchus enter, so as 

 to form a parietal layer lining its 

 half of the thoracic cavity. The 

 median space between the two 

 sacs is called the mediastinum. 

 The anterior or ventral medias- 

 tinum contains the heart. The 

 dorsal or posterior mediastinum 

 contains the esophagus and 

 aorta. 



Each lung is divided by deep clefts into several lobes. 

 The left lung is composed of two large lobes and a small 

 one. The right lung consists of four unequal lobes. The 

 cephalic end of the lung is the apex and the caudal end, 

 resting against the diaphragm, is the base. The bronchi, 

 as they are continued into the lungs, subdivide into 

 smaller tubes, whose later subdivisions are the bron- 

 chioles. The latter, dividing like the branches of a tree, 

 finally terminate in blind pouches known as infundibulo 

 or alveoli, the walls of w T hich are thickly beset with 

 microscopic sac-like evaginations named air sacs (Figs. 



FIG. 82. THE TERMINATION 

 OF THE BRONCHIOLE c IN 

 FIG. 81. 



br, Bronchiole; al, alveolus 

 showing about a dozen air 

 sacs or air cells. (From 

 Martin's " Human Body.") 



