116 



RESPIRATION RESPIRATORY MOVEMENTS. 



FIG. 44. Thorax, anterior view (Sappey). 



1, 2, 3, sternum ; 4, circumference of the upper 

 portion of the thorax ; 5, circumference of 

 the base of the thorax ; 6, first rib ; 7, sec- 

 ondrib; 8, 8, last five sternal ribs; 9 up- 



to the increased capacity of the lungs. In the mammalia, the chest is en- 

 larged by the action of muscles ; and in ordinary respiration, inspiration is 



an active process, while ordinary expira- 

 tion is passive. 



A glance at the physiological anato- 

 my of the thorax in the human subject 

 makes it evident that the action of cer- 

 tain muscles will considerably increase its 

 capacity. In the first place, the dia- 

 phragm mounts up into its cavity in the 

 form of a vaulted arch. By contraction 

 of its fibres, it is brought nearer a plane, 

 and thus the vertical diameter of the 

 thorax is increased. The walls of the 

 thorax are formed by the dorsal vertebrae 

 and ribs posteriorly, by the upper ten 

 ribs laterally, and by the sternum and 

 costal cartilages anteriorly. The direc- 

 tion of the ribs, their mode of connection 

 with the sternum by the costal cartilages,. 

 and their articulation with the vertebral 

 column, are such that by their move- 

 ments, the antero-posterior and trans- 

 verse diameters of the chest may be considerably modified. 



Inspiration. The ribs are somewhat twisted upon themselves and have a 

 general direction forward and downward. The first rib is nearly horizontal, 

 but the obliquity of the ribs progressively 

 increases from the upper to the lower 

 part of the chest. They are articulated 

 with the bodies of the vertebras, so as to 

 allow of considerable motion. The up- 

 per seven ribs are attached by the costal 

 cartilages to the sternum, these cartilages 

 running upward and inward. The car- 

 tilages of the eighth, ninth and tenth 

 ribs are joined to the cartilage of the sev- 

 enth. 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 bor- , , mMgmo , 



der of each rib and attached to the up- BSJETO^^ * 



FIG. 45. Thorax, posterior view (Sappey). 



