DISEASES OF KESPIEATORY ORGANS 147 



Larynx. — The larynx is long and has considerable mobility, due 

 to the relatively loose attachments of the laryngeal cartilages. The 

 vocal cords extend obliquely downward and backward. They are 

 close together and hence the rima glottidis is narrow. Bach vocal 

 cord has an opening communicating with the laryngeal saccules. 



Trachea and Bronchi. — The trachea extends from the larynx down- 

 ward along the inferior portion of the cervical region into the 

 thoracic cavity where it bifurcates, forming the bronchial tubes. 

 The trachea is six to eight inches in length and contains about 

 thirty-five incomplete cartilaginous rings. '' 



There are two principal bronchial tubes, one being distributed to 

 the right and the other to the left lung. A small tube is detached 

 and is distributed to the right apical lobe of the lung. The prin- 

 cipal bronchus of "the right lung supplies branches to the cardiac 

 and intermediate lobes and then continues into, and is distributed 

 to the diaphragmatic lobe. The left principal bronchus supplies a 

 branch that subdivides and is distributed to the apical and cardiac 

 lobes and then continues and supplies the diaphragmatic lobe. 



Lungs. — The right lung is usually divided into four lobes: apical, 

 cardiac, intermediate, and diaphragmatic. The left lung Jias two 

 distinct lobes and some anatomists describe a third indistinct lobe. 

 In the left lung the diaphragmatic lobe is distinct. ' In the anterior 

 portion the apical and cardiac lobes are usually fused. 



The lung lobules are distinct but the interlobular tissue is limited. 

 ■ Thyroid gland. — This gland is relatively large and is usually well 

 removed from the larynx. The lateral lobes are two inches or more in 

 length, are rather irregular and well united. 



Thymus gland. — This gland is large in the pig, extending from the 

 larynx into the thoracic cavity, but it gradually atrophies and is a 

 mere rudiment in the adult. 



Pleura. — The pleural sacs comprise a double foJ,d of serous mem- 

 brane, the outer or parietal layer being attached to the inner wall of 

 the thorax, diaphragm, and is deflected downward from the dorsal 

 median line. The inner or visceral portion is 'reflected over and 

 closely attached to the outer surface of the lungs. 



Respiration 



By respiration is ordinarily understood the exchange of air 'in 

 the lungs. The purpose of respiration is for the introduction of 



