122 



THE ANATOMY OF THE HOESB. 



costal arteries. This series is continued by branches of the asternal 

 artery. 



The Internal Thobacic Vein runs in company with the artery, and 

 internal to it. Beneath the triangularis sterni it is placed between the 

 artery and the fibrous cord that traverse the edge of the sternum. 



SuPRASTEBNAL Ltmphatic Glands. These include (1) a group of 

 glands on the thoracic side of the insertion of the diaphragm across the 

 ensiform cartilage, and (2) some small scattered glands along the course 

 of the internal thoracic vessels. 



examination of the lung. 

 Physical Characters. — The exterior of the lung is exquisitely smooth 

 in virtue of its pleural covering. Through this thin, transparent 



covering, the surface is seen, 

 especially when the lung is dis- 

 tended, to be divided by inter- 

 secting lines into small areas, each 

 of which corresponds to a lobule 

 of the lung. The lines are 

 formed by the interlobular con- 

 nective-tissue. 



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 is of a 

 grayish or slaty hue. In the 

 fcetus 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 distend- 

 ing force is removed. It crepi- 

 tates on pressure with the 

 fingers, and it floats on water. 

 The foetal lung is non-crepitant, 

 and sinks in water. 



Structure. — When the bronchus enters the lung, it divides again and 

 again until there results a remarkable tree-like arrangement of bronchial 

 tubes. Of this tree, the bronchus 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 



Fig. 8. 



Termination of the Air Passages in the Lung 

 (modified from Titnier). 



A, A. Terminal bronchioles ; B. An inf undibulum, 

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

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

 laries. 



