472 



THE RESPIRATORY APPARATUS IN MAMMALIA. 



Internally, the human larynx has no subepiglottic or subarytenoid sinus like that of 

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

 of the superior vocul 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 lias 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 lungs 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. 



Fte. 243. 



THE GLANDIFORM BODIES CONNECTED WITH THE RESPIRATORY APPARATUS. 



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. 



STRUCTURE. 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 laminas 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 youtig 

 animal, they are round or ellip- 

 tical, and constituted by a thin 



GROUP OF GLAND VESICLES FROM THE THYROID -, -, v J i 



BODY OF A YOUNG SUBJECT. amorphous membrane, lined by 



a, Connective tissue; 6, Basement membrane of polygonal cells With a large nu- 



the vesicles ; c, Epithelial cells. cleus, and containing a granular 



fluid. In the adult, these vesicles 

 are deformed, and, after being distended, several are confounded together; 



