92 NON-SPECIFIC OR GENERAL DISEASES 



TJie larynx may be compared to a box open at both ends. 

 The several cartilages that form it are united by ligaments. It 

 is lined by a mucous membrane. The posterior extremity is 

 united to the first cartilaginous ring of the trachea. The 

 anterior opening is closed by the epiglottis. Just within is a 

 \'-shaped opening that is limited laterally by the folds of the 

 laryngeal mucous membrane, the vocal chords. 



The tracliea is a cylindrical tube originating at the posterior 

 extremity of the larynx, and terminating within the chest cavity 

 at a point just above the heart in the right and left bronchial 

 tubes. It is formed by a series of cartilaginous rings joined 

 together at their borders by ligaments and lined by a mucous 

 membrane. 



The hronchial tuhes resemble the trachea in structure. They 

 enter the lungs a short distance from their origin, where they 

 subdivide into branches and sub-branches, gradually decreasing 

 in calibre and losing the cartilaginous rings, ligaments and 

 muscular layer until only the thin mucous membrane is left. 

 They become capillary in diameter, and finally open into the 

 infundibula of the air cells of the lungs. 



The lungs take up all of the space in the thoracic cavity not 

 occupied by the heart, blood-vessels and oesophagus. This cavity 

 resembles a cone in shape that is cut obliquely downwards and 

 forward at its base. The base is formed by the diaphragm which 

 is pushed forward at its middle. It is lined by the pleura, a 

 serous membrane, that is inflected from the wall over the differ- 

 ent organs within the cavity. The median folds of the pleura 

 divide the cavity into right and left portions. A second method 

 of describing the arrangement of the pleura is to state that it 

 f()i"ms two sacks, right and left, that enclose the lungs. The 

 lungs are the essential organs of respiration. The tissue that 

 forms them is light, will float in water, is elastic and somewhat 

 rose-colored. Each lung is divided into lobes, and each lobe into 

 a great number of lobules by the supporting connective tissue. 



