552 RESPIRATORY APPARATUS IN MAMMALIA. 



of these spaces. With the intimate mechanism of these actions we have nothing 

 to do here, however. 



Development. — Although the lung is in a state of inactivity in the foetus, 

 yet it is one of the early developed organs. During the whole period of foetal 

 existence, its lobular texture is much better defined than in the adult, and it 

 then appears to be formed exactly like a racemose gland. Sections of it prepared 

 for microscopical examination, distinctly show the vesicles and their arrangement. 

 We have already made known the differences in colour and density which dis- 

 tinguish the pulmonary tissue of the foetus and that of the adult. It only 

 remains to repeat what has been said as to the slight vascularity of the first, 

 and to note that the blood of the pulmonary artery passes almost entirely into 

 the posterior aorta by the arterial canal (or ductus arteriosus). 



Differential Characters in the Lungs of the other Animals. 



The form of the lungs of Ruminants does not differ from that of the Horse, except thnt 

 fie left is divided into two lobes, and the right into four — the anterior of tliese being curved 

 in front of the heart. This is shown in Fig. 332. 



The lungs of the Ox, Sheep, and Goat are remarkable for tlie distinctness with whicli 

 the lobules are defined. They are, in fact, separated by loose connective tissue, which, by a 

 certain degree of traction, may extend 1 or 2 millimetres ; it forms a reticular and alveolar 

 system capable of being developed by insufflation. Eenant and Pierret have shown that the 

 dilatable tracts are lymph spaces, lined with a characteristically festooned epithelium ; so that 

 the pulmonary lobules in the lung of the Ox are bathed in a lymphatic sac. 



As a consequence of inflammation, these spaces, are gorged with tibrin(^ and leucocytes, and 

 contrast strikingly, by their pale tint, witli the lobules; therefore the lesions of pneumonia in 

 the larger Ruminants have an altogether special character—a fact to which Dietrichs drew 

 attention a long time ago. 



In the Pig, the lungs comport themselves somewhat like those of Ruminants. 



In the Dog and Cat, there is no well-marked fissure in either lung towards the heart, 

 which causes that organ to be almost completely enveloped by pulmonary tissue. The left 

 lung has three lobes, and the right four, separated from one another by deep furrows, which 

 are generally prolonged to the root. The lobules are small, very close, and the pulmonary 

 tissue is exceedingly compact. (The pulmonary infundibula are proportionately larger than in 

 Ruminants.) 



Comparison of the Larynx, Trachea, and Lungs of Man with those of Animals. 



1. Larynx. — The human larynx is proportionately shorter and wider than that of animals. 

 The principal cartilages are those which have been already studied ; but there are, besides, 

 small cartilaginous bodies, to which special names have been given : these are the cartilages of 

 Santorini and of Wrisberg. The facets on the cricoid for articulation with the thyroid are 

 placed on the small cornu detached from the external face of the cartilage. Tiie thyroid is 

 wide, and protects the anterior face of the larynx ; the angle formed by the alse, which is more 

 marked in the male than the female, is very prominent, and is named the pomum Adanii. 

 The epiglottis is short, broad in its middle, and rounded at its summit, something like that of 

 the Carnivora. The muscles are the same in number and disposition as in these animals ; but 

 there is distinguished an oblique arytsenoideus — a fasciculus of the arytsenoid, which crosses its 

 fellow to form an X in passing from the upper border of one arytsenoid cartilage to the lower 

 border of the other. 



Internally, the human larynx has no sub-epiglottic or sub-arytsenoid sinus like that of Soli- 

 peds, though it luis lateral, or Morgagni's, ventricles that ascend 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 arc 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 tlie thyroid gland ; at its entrance into 

 the chest it deviates slightly to the right. The two «hort canals between its lower extremity 



