124 



THE ANATOMY OF THE HORSE. 





divided by delicate intersecting lines into small areas, each of which 

 corresponds to a lobule of the lung. The lines are formed by the inter- 

 lobular connective-tissue, which in the horse is very sparing in 

 amount. 



The colour of the lung varies with the age of the animal. In the 

 young subject it is pale pink, but in old animals it has a slight grayish 



or slaty tinge. In the foetus 



_p it is a bright pink. 



The lung is spongy to the 

 touch, and its cut surface has 

 the same appearance. It is 

 also markedly elastic, this 

 quality being best illustrated 

 by the rapidity with which the 

 inflated lung collapses when 

 the distending forceisremoved. 

 It crepitates on pressure with 

 the fingers, and it floats on 

 water. The foetal lung is 

 non-crepitant, and sinks in 

 water. 



Structure. — When the bron- 

 chus enters the lung, it divides 

 again and again until there 

 results a remarkable tree-like 

 arrangement of bronchial 

 tubes. Of this tree, the bron- 

 chus entering the root of the 

 lung forms the main stem ; 

 and, as the division is traced 

 onwards, the bronchial tubes, 

 representing the branches, become smaller and smaller, until there 

 is reached a tube of comparatively small calibre which belongs 

 exclusively to one lobule, and is therefore termed a lobular or terminal 

 bronchus. The left bronchus has a length of three or four inches before 

 dividing, but the right immediately gives off from its outer side a con- 

 siderable branch (Plate 26). Within each lobule the terminal bronchus 

 ramifies, forming smaller tubes or bronchioles, the last and smallest of 

 which leads into recesses or dilatations. Each such dilatation is termed 

 an alveolar passage, and it is bounded by delicate sacculated walls, 

 each sacculation being an infundibulum. The infundibula are them- 

 selves sacculated, the minute recesses of their walls being termed 

 air-cells. The air-cell is thus the ultimate part of the air passages 

 within the lung, and a group of air-cells forms an infundibulum. The 



Fig. 8. 



Teemination of the Ate Passages in the Lung 

 (modified from Turner). 



A. A. Terminal "bronchioles ; B. An infundibulum, 

 showing the air-cells on its surface ; C. Pulmonary 

 artery ; D. Pulmonary vein ; E. Pulmonary capil- 

 laries. 



