102 



A MANUAL OF VETERINARY PHYSIOLOGY 



upper part, and on this the actual width of the^back depends. 

 From the ninth to the eighteenth the ribs decrease in length. 

 The respiratory portion of the thorax extends from the seventh 

 to the eighteenth rib. The movement of the ribs is mainly of 

 two kinds. At their upper part they are partly everted and 

 pulled forwards, below they are thrust outwards. The curva- 

 ture of the rib is turned to account when it attempts the process 

 of eversion, for by means of this movement very little eversion 



represents a distinct in- 

 crease in the transverse 

 diameter of the chest 

 cavity. The semicircle 

 formed by the cage is 

 well seen in vertical sec- 

 tion in Fig. 42, A and B, 

 made at the anterior and 

 posterior part of the 

 thorax. 



A front to rear section 

 of the chest (Fig. 43) is 

 roughly egg - shaped, the 

 narrow end of the egg in 

 front, while the broad end 

 is cut off obliquely for a 

 considerable distance in 

 the position occupied by 

 the diaphragm. Of the 

 Matter we shall speak in 

 detail presently, but it may 

 be noted that the move- 

 ments of the diaphragm 

 and the other muscles of 

 inspiration are capable 

 during quiet respiration of 

 lengthening the front to 

 rear diameter of the chest 

 by 10 to 12 cm. (4 to 5 

 inches), while at the widest 

 part of the chest wall — 

 viz., between the eleventh and twelfth ribs — the increase in 

 side to side diameter is about 4 cm. (ij- inches). 



Movements of the Diaphragm. — The vast musculo-tendinous 

 sheet placed between the abdominal and thoracic cavities merits 

 detailed consideration, owing to its importance in the respiratory 

 mechanism. This muscle is placed obliquely forward in the 

 body, and extends from the region of the loins to the sternum. 



Fig. 43. — Horizontal Section of the 

 Horse's Chest looked at from Above 

 (Sussdorf-Ellenberger). 



a, Right lung ; b, left lung ; i, position of the 

 diaphragm during deep expiration ; c, 

 liver during deep expiration ; d, stomach 

 during deep expiration ; e, spleen during 

 deep expiration ; 2, position of dia- 

 phragm during deep inspiration ; c', 

 position of liver ; d', of stomach ; e', of 

 spleen during deep inspiration ; /, pos- 

 terior vena cava as it passes through the 

 diaphragm. 



