SECT. 1 75-] TI1E LUNGS AND PLEURJE. 38 1 



vesicles (p'002'" to o - oo3'" in diameter), and a very narrow 

 aperture with thick walls (o'Oo6'" to croi'"), the appearance of 

 thickness resulting from a beautiful cylindrical epithelium. 



The blood vessels of the trachea arc very numerous; those of the 

 mucous membrane exhibit the peculiarity of the larger branches 

 running chiefly in the longitudinal direction, while the net-work 

 formed by the superficial capillaries, has roundish or angular 

 meshes. This superficial net-work is frequently situated imme- 

 diately beneath the homogeneous layer of the mucous membrane, 

 external to the elastic elements. The trachea possesses a large 

 number of lymphatic-vessels, whose mode of commencement is not 

 known with certainty. That which I formerly described as such 

 (Mi/-. Anat. ii. 2, p. 307), was, probably, only some peculiar alter- 

 ation in the blood-vessels (see ibid. p. 526). Numerous nerves also 

 ait 1 found in the trachea, which have the same arrangement here 

 as in the larynx. 



§ 175. Lungs. — The lungs are two large compound racemose 

 glands, in which there may be distinguished, 1, a special serous 

 envelope, the pleura ; 2, the secretory parenchyna, consisting of 

 the ramifications of the two bronchi, with their terminations — the 

 air-cells, together with numerous vessels and nerves; and, 3, 

 an interstitial tissue, situated between these parts, and connecting 

 them into larger and smaller lobules. 



The pleurcs completely agree in their structure with the peri- 

 tonaeum ; like this, they are thicker in their parietal lamina, and 

 consist of connective tissue, richly furnished with elastic elements, 

 some finer and some coarser, which tissue is covered by a pave- 

 ment-epithelium. To these components is added, in the pleura 

 covering the thoracic walls and the outside of the pericardium, a 

 more purely fibrous layer. Vessels are seen in the pleura, most 

 abundantly in that covering the lung, where they are furnished to 

 tlii* subserous tissue from the bronchial and pulmonary arteries; 

 the parietal lamellaj are supplied more scantily by the intercostal 

 and mammary vessels. Luschha has found nerves with fine and 

 broad tubules, and has traced them in the outer part of the 

 pleura to the phrenic nerve and the thoracic part of the sym- 

 pathetic. I also have observed nerves in the pulmonary pleura 

 of man, measuring up to o"036'" in diameter, and accompanying 

 the bronchial arteries ; they possessed nerve-tubes, some thick 

 and others moderately fine, and here and there were inter- 

 spersed large ganglion-globules, which came from the pulmonary 



