952 



A MANUAL OF ANATOMY 



called the cparterial bronchus, for the upper lobe of the right lung and 

 beyond this point, where it is now hyparterial, it divides into two branches 

 one for the middle, and the other for the lower, lobe. The left bronchus is 

 entirely hyparterial. and divides into two branches, one for the upper and 

 the other for the lower, lobe of the left lung. The structure of these primary 

 divisions of the brorcni is similar to that of the bronchi themselves. Within 

 each lung these^ primary divisions undergo subdivision, to a certain extent 

 dichotomously, .^ut the ramifications are chiefly due to branches being given 

 oil laterally, and these never anastomose. The ramifications of tlie air- 

 tubes within the lungs are called the bronchial tubes, and their ultimate 

 subdivisions within the lobules are known as the bronchioles. Each bron- 

 chiole transmits air to and from a group of infundibula, or ultimate lobules. 

 _ haen lobular bronchial tube, after entering a lobule, divides into as many 

 Dronchioles as there are groups of infundibula or ultimate lobules. Each 



Infundibulum or 

 Ultimate Lobule 



.-Bronchiole 

 Intercellular Septum 



Air Cell 



Lobular Bronchial Tube 



* Vestibule 



Fig. 390.- 



-SCHEME OF A PuLMONARY LOBULE (AFTER L. TeSTUT's 



'Anatomie Humaine'). 



bronchiole, on approaching a cluster of, say, two or three infundibula, pre- 

 sents a dilatation, called the vestibule, and from this vestibule reception- 

 chambers, known as the atria, proceed to the infundibula. 



An infundibulum or ultimate lobule is an irregular, funnel-shaped passage, 

 closed at one end, and having its walls and closed extremity beset with 

 air-cells or pulmonary alveoli, which also beset, though more sparsely, the 

 walls of the atria. 



The bronchial tubes within the lungs are destitute of membranous walls 

 posteriorly, and are cylindrical. This is due to the fact that their irregular 

 plates of cartilage are disposed round the circumference of the wall. The 

 muscular fibres are arranged in complete rings round the tubes, and the 

 elastic tissue forms longitudinal bundles. The mucous membrane is freely 

 provided with racemose mucous glands, and is covered with stratified ciliated 

 columnar epithelium. When the tubes, by division, have attained a diameter 

 of about vj>5 inch, the cartilaginous plates disappear, and the walls consist of a 



