PIGEON. 27 



THE DIAPHRAGM 



Is incomplete, and is attached to the ribs outside the borders of 

 the lungs and from the spinal column, and ends by an aponuerotic 

 expansion upon the ventral surface of the lungs. The lungs are 

 two in number, and extend from the second dorsal vertebra to 

 the kidneys, and laterally to the junction of the sternal with the 

 vertebral ribs. The pleura is reflected only over the sternal 

 surface of the lungs. 



Each bronchus, as it enters the lung, immediately loses its 

 cartilaginous rings, and, after traversing the lung, ends at its 

 posterior part by opening into one of the abdominal air sacs. Canals 

 are given off from the inner side of the bronchus, which pass to the 

 under surface of the lung, and there open into other air sacs. Of 

 these there are altogether nine — two abdominal, before mentioned, 

 two anteriorly and two posterior thoracic, one clavicular, and two 

 cervical. All these air sacs, except the anterior and posterior 

 thoracic, communicate with an extensive system of air passages,. 

 which ramify through most of the bones of the skeleton with the 

 exception of the bones of the skull, which receive their air from 

 the nasal chambers and tympana. 



LARYNX. 



In the pigeon, as in all birds, there are distinct thyroid, cricoid,, 

 and argtenoid cartilages. The voice is not produced in the larynx, 

 however, but in the lower larynx or syrinx. This is situated at 

 the lower end of the trachea, at its point of division into the two 

 bronchi. The syrinx is a complicated apparatus of cartilages and 

 bones, regulated by appropriate muscles. It is developed at the 

 junction of the trachea and bronchi, and from both — hence it is- 

 known as the broncho-tracheal form of syrinx. 



CIRCULATORY SYSTEM. 



HEART 



Is cone-shaped, and consists of two auricles and two ventricles. 

 Its apex is placed between the two lobes of the liver. As the 

 lungs are situated dorsally, the whole anterior surface of the 

 pericardium is brought into view when the sternum is removed. 



The pericardium surrounds the heart, and adheres by its external 

 surface to the neighbouring air cells. The heart is of large size, 

 and is continued for some distance between the lobes of the liver. 



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