548 



RESPIRATORY APPARATUS IN MAMMALIA. 



lobule. It forms a small pyramid with a polygonal base, measiirins: about ^ of a 

 cubic inch, and is sm-rounded by a layer of connective tissue which unites it to 

 the neighbouring lobules, and in which are some lymphatics and the network 

 formed by the pulmonary vein. It appears to be suspended by its summit to a 

 very short pedicle consisting of : 1. A sublobular bronchiole of about 0'039 inch 

 in diameter. 2. A twig of the bronchial artery. 3. A branch of the pulmonary 

 artery. 4. A division of the pulmonary vein. While the first three elements of 

 the pedicle enter the lobule, the fom-th deviates suddenly and becomes a capillary 

 network on its outer surface. 



In the lobule, the sublobular bronchule is named the intra-lobular bronchiole; 

 it gives off the lateral intra-lobular hi^onchioles in passing towards the base of the 

 lobule, where it throws off at last two terminal bronchioles. Each lateral bron- 

 chiole comports itself like the intra-lobular one, and terminates in the same 



Fig. 326. 



LUNG OF THE HORSE RESTING ON ITS DIAPHRAGMATIC SURFACE, AND VIEWED BY ITS ANTERIOR 



EXTREMITY. 



T, Trachea ; D, right lobe ; G, left lobe ; L, anterior lobule of the right lobe ; L', anterior lobule 

 of the left lobe ; Ap, branches of the pulmonary artery at their entrance into the two lobes ; 

 F, F', notch on the right and left of the inferior border of the lung, in face of the heart; E, notch 

 on the upper border for the passage of the aorta ; V, V, openings of the pulmonary veins ; La, 

 lobule of the right lung ; S, fissure for the passage of the posterior vena cava. 



manner — by two short or acinous bronchioles, about ^^ of a millimetre in 

 diameter. 



At the extremity of each of the terminal bronchioles — short or acinous — is 

 suspended a small pyramidal mass of 2 to 3 cubic millimetres — the acinus., which 

 at first showing an initial dilatation — the vestibule, afterwards gives off three, 

 four, or five divergent tubes of from ^ to f of a millimetre — the alveolar passages, 

 or, better, respiratory canaliculi. These are sacculated on their surface and 

 expanded at their termination, so as to resemble small bunches of grapes in 

 which the fruit is not very distinct from the stalk. The terminal dilatations are 

 named infundihnla, and the boss-like portions alveoli, or pulmonary vesicles. 



The ramifications of the bronchial artery are expended in the tissue of the 

 bronchioles, and do not extend beyond the commencement of the alveoli and 

 infundibula ; while the branches of the pulmonary artery accompany the bronchi, 

 and become capillaries in the walls of the alveoli and infundibula. In this way 



