198 ANATOMY OF THE DOMESTIC FOWL 



ward, and the fourth directly backward. They have, by some 

 anatomists, been called the anterior, the internal, and the pos- 

 terior diaphragmatic bronchial tubes. There are two posterior 

 diaphragmatic bronchial tubes; the larger called the great pos- 

 terior, and the smaller, which passes directly backward, the small 

 posterior. 



The costal bronchial tubes, seven in number, are numbered from 

 the front backward in the order they are given off. Parallel at 

 their origin, and side by side, like pipes of an organ, they soon spread 

 out in fan shape like the preceding. They extend from their cen- 

 tral origin to the periphery. The first extends obliquely upward 

 and inward to the anterior extremity of the lung. All branches 

 from this bronchus extend from its anterior wall. The first branches 

 are inflected to reach the external border of the lung. The succeed- 

 ing branches are directed forward and the last forward and inward. 

 They all meet those from the anterior diaphragmatic bronchus, 

 but do not anastomose with them. 



The second, the third, .and the fourth costal bronchi extend in a 

 transverse manner and ramify on the inner border of the lung. 



The fifth and the sixth are directed toward the posterior extremity 

 of the lung. The seventh, very small, reaches this extremity, where 

 it disappears. 



The first costal bronchus is the largest; those following it gradually 

 become smaller. At their points of origin they adhere closely to 

 the ribs. They are all imperforate, which is a distinguishing fea- 

 ture from those occupying the opposite face. 



The canaliculi or tertiary tubules given off by these secondary 

 bronchial tubes do not differ greatly in caliber in the various parts. 

 They are given off at right angles from the pulmonary wall of each 

 bronchus, and extend perpendicularly into the lung substance. 

 Thus we find three kinds of conduits, the primary, the secondary, 

 and the peripheral, or tertiary. The first are like the barbs of a 

 feather on its shaft; and the second, and parenchyma tous are im- 

 planted on the pulmonary walls of the first, like the hairs of a 

 brush on their common base. Thus instead of the branching of 

 the bronchi being dichrotomous, as in mammals, it is piniform. 



The canaliculi, or finer tubules, communicate with one another. 

 The inner microscopic appearance of the canaliculi indicate that 

 they are divided into areola, which gives them a cellular aspect 

 These tertiary bronchi open on a dense labyrinth of blood capillaries 



