IOO 



A MANUAL OF VETERINARY PHYSIOLOGY 



This table shows how rapidly the chest increases in width irom 

 front to rear, and the rate of that increase from rib to rib. If a 

 vertical section of the chest be made — say between the fifth and 

 sixth ribs — the thoracic cavity will be found egg-shaped, the 

 broad part being above, the wall curving inward to obtain a 

 hold in the sternum. From the first to the sixth rib the main 

 function of the chest wall is to form a case for the vascular 

 apparatus and to support the horizontal spine. The lateral 



Fig. 40. — First Pair of Ribs 

 in the Horse (after 

 Schmaltz : Atlas d. Anat. d. 

 Pferdes). 



It will be noted the way in 

 which the head and tubercle 

 are disposed in order to prop 

 up the spine. 



Fig. 41. — Head of the Eighth and Six- 

 teenth Rib of the Horse (after 

 Schmaltz: Atlas d. Anat. d. Pferdes). 



A is the eighth rib in normal position ; the 

 tubercle is still above the head. B is 

 the sixteenth rib in position ; the tuber- 

 cle now lies behind the head, and cannot 

 be seen from the front. 



movements of the sternal ribs is of no importance from a respira- 

 tory point of view. Some, like the first pair (Fig. 40), have 

 no lateral movement, and it is very limited in the others, though 

 it increases as we pass further back in the chest. Under forced 

 respiration the fifth rib might take a limited share in respiration, 

 but practically none of those anterior to it have any movement. 

 The relatively rigid cage formed by the first to the sixth ribs 

 articulates with the spine, and it might be supposed that some 

 rib movement favourable to respiration must occur, or the ribs 



