9 6 



RESPIRATION 



these cartilages running upward and inward. The cartilages of the 

 eighth, ninth and tenth ribs are joined to the cartilage of the seventh. 

 The eleventh and twelfth are floating ribs and are attached only to the 

 vertebrae. 



It may be stated in general terms that inspiration is effected by 

 descent of the diaphragm and elevation of the ribs ; and expiration, by 

 elevation of the diaphragm and descent of the ribs. 



Arising severally from the lower border of each rib and attached to 

 the upper border of the rib below, are the eleven external intercostal 

 muscles, the fibres of which have an oblique direction from above down- 



Fig. 31. Thorax, anterior view (Sappey). 



I, 2, 3, sternum ; 4, circumference of the upper 

 portion of the thorax ; 5,' circumference of the base 

 of the thorax ; 6, first rib ; 7, second rib ; 8, 8, last 

 five sternal ribs ; 9, upper three false ribs ; 10, last 

 two, or floating ribs; n, costal cartilages. 



Fig. 32. Thorax, posterior view (Sappey). 



i, i, spinous processes of the dorsal verte- 

 brae; 2, 2, laminae of the vertebrae; 3, 3, trans- 

 verse processes ; 4, 4, dorsal portions of the ribs ; 

 5, 5, angles of the ribs. 



ward and forward. Attached to the inner borders of the ribs, are the 

 internal intercostals, which have a direction from above downward and 

 backward, nearly at right angles to the fibres of the external intercos- 

 tals. There are also certain muscles attached to the thorax and spine, 

 thorax and head, upper part of humerus etc., that are capable of ele- 

 vating either the entire chest or the ribs. These act as muscles of inspi- 

 ration when the attachments to the thorax become the movable points. 

 Some of them are called into action during ordinary respiration ; others 

 act as auxiliaries when respiration is moderately exaggerated, as after 

 exercise, and are called ordinary auxiliaries ; while others, which ordi- 



