472 



TEE BESPIRATOBT APPABATUS IN MAMMALIA. 



Internally, the humaQ larynx has no subepiglottio or subarytenoid sinus like that of 

 Solipeds, though it has lateral, or Morgagni's, ventricles that uscend a little to the outside 

 of the superior vocal cords. 



2. Trachea. — 3. Bronchi. — There is little difference to be remarked in these. The 

 trachea is about four inches long and about one inch wide, and is composed of about 

 twenty C-shaped rings, which are closely united, as in animals. It is situated in the 

 median plane, in the upper part of the neck, where it is embraced by the lobes of the 

 thyroid gland ; at its entrance into the chest it deviates slightly to the right. The two 

 short canals between its lower extremity and the lungs are the bronchi; the right 

 bronchus is the shortest and widest, and Las an almost horizontal direction, entering 

 the right lung at the fourth dorsal vertebra; the left is longer and less voluminous, and 

 reaches the corresponding lung at the fifth vertebra. 



4. Lungs. — The luugs weigh about forty ounces. As in all animals, the right is 

 more voluminous than the left, and is divided into three lobes ; the latter has only two. 

 The inferior vena cava is not surrounded by pulmonary tissue ; the principal lobes are 

 partitioned into lobules, which are visible on the surface, and on the limits of which 

 are deposited, only in the adult, a notable quantity of pigmentary matter, that gives the 

 lungs the appearance of a chess-board. There is nothing to be said respecting their 

 internal conformation and structure. 



THE GLANDIFOHM BODIES CONNECTED WITH THE KESPIBATOEY APPAKATtTS. 



1. Thyroid Body (or Gland). 



The thyroid gland, or body, is composed of two oval lobes of a reddish- 

 brown colour, and 'is situated close to, and behind, the larynx, beside the two 

 first rings of the trachea. 



These two lobes, distinguished as right and left, appear at first sight to 

 be perfectly independent ; but a less superficial examination shows them to 

 be united by an intermediate portion (the isthmus), which passes across the 

 anterior face of the trachea. 



Each lobe of the .thyroid body corresponds, inwardly, to that tube ; 

 outwardly, it is covered by the subscapulo-hyoid muscle. 



Fl^ 243. . Steuctukb.— The thyroid body 



is composed of a fibrous envelope, 

 and a proper tissue or parenchyma. 

 The fibrous envelope is composed 

 of slender, but strong connective 

 tissue; it sends from its inner 

 face a large number of thin nu- 

 cleated lamiuEe that intersect each 

 other, forming spaces in which the 

 proper tissue is contained. 



The parenchyma is divided into 

 lobules, whose presence is mani- 

 fested on the surface of the organ. 

 They are composed of vesicles, the' 

 shape and contents of which vary 

 considerably with age and situa- 

 tion. In the foetus, or very young 

 animal, they are round or ellip- 

 tical, and constituted by a thin 

 amorphous membrane, lined by 

 polygonal cells with a large nu- 

 cleus, and containing a granular 

 If T -,„,,. fluid. In the adult, these vesicles 



are deformed, and, after being distended, several are confouiided Lgether! 



GROUP OF GLAND VESICLES FEOM THE THYROID 



BODY OF A TOUNG SUBJECT. 



a, Connective tissue ; 5, Basement membrane of 



tie vesicles ; c, Epithelial cells. 



