272 



THE HORSE. 



which are bound down by white fibrous tissue at the points -where 

 the strain is the greatest. In the limbs the muscles are bound up 

 into masses by strong but thin layers of intercrossed white fibrous 

 tissue, which receives the name of fascia. In the horse this ie 

 very firmly attached to the surface of the muscles beneath, and 

 greatly interferes with the clean dissection of them. 



CHAPTER XVI. 



THE THOKAX. 



Contents of the Thorax — The Blood — General Plan of the 

 Circulation—^ The Feins — Physiology of Respiration. 



CONTENTS OF THE THORAX. 



The thokax, or chest, is that cavity formed by the bodies of 

 the dorsal vertebrae superiorly; by the ribs and their cartilages 

 with the connecting muscles laterally; by the sternum inferiorly; 

 by the diaphragm posteriorly; and by the inner margins of the first 



ribs and body of the first dorsal 

 vertebra anteriorly. It contains 

 the central parts of the import- 

 ant organs of circulation and 

 respiration, and gives passage to 

 the oesophagus, as it connects 

 the pharynx with the stomach. 

 As these lie within it, they are 

 allowed to play freely in per- 

 forming their functions, by being 

 enveloped by smooth serous mem- 

 branes, called the pleura and the 

 pericardium, the latter being 

 also protected by a fibrous layer. 

 A section of the thorax, as shown 

 in the plan, fig 10 will give some 

 idea of the relative situation of 

 these organs and their invest- 

 ments, as well as of the shapo of 

 the cavity itself in this direction. 

 The heart is shown at A, lying 

 between the two bags of the 

 pleura, in the space called the 

 mediastinum. The lungs are shown at B B, covered by a fine 

 serous membrane (H H), pleura pulmonalis, except at their roots, 



llfl. 10. — SECTIONAL PLAN OF THORAX AND ITS 

 CONTENTS (THROUGHOUT ITS GIRTH-PLACE). 



A. Heart. 



B. B. Lungs. 



0. E. D. F. Walls of the thorax. 

 G. Q. Pleura costalis. 

 If. H. Pleura pulmooalis. 



