THORACIC MOVEMENTS. 327 



A new-born infant . . . respires 44 times per minute. 



5 years, ... " 26 " " 



1520 " ... "20 " " 



2025 " ... " 18.7 " 



2530 " ... "16 " " 



3060 " ... " 18.1 " " 



Muscular exercise increases the rapidity of the respiratory 

 movements, and, consequently, the effort of standing produces a 

 more frequent respiration than is found in the recumbent posture. 

 Emotions variously affect the rate and rhythm of the inspiration 

 and expiration (e.g., sighing) ; and, finally, morbid conditions, 

 implicating the lungs, usually cause a greater frequency of respi- 

 ration, sometimes attaining a rate of as many as 60-70 respira- 

 tions per minute. 



The thorax is enlarged in all directions during inspiration, the 

 motion being usually referred to the vertical, transverse, and an- 

 tero-posterior diameters respectively. 



The vertical diameter is increased by the descent of the lateral 

 parts of the diaphragm, and the slight elevation of the parts about 

 the apex. 



The lateral diameter is widened by the side-droop of the ribs 

 being lessened ; each rib is rotated upon the line uniting its ex- 

 tremities, and at the same time is moved upward and outward. 



The antero-posterior diameter is enlarged by the general eleva- 

 tion of the ribs and sternum, the anterior extremities of the ribs, 

 being drawn up from their general downward incline, push the 

 sternum forwards. 



The movements of the diaphragm depress the abdominal vis- 

 cera lying beneath it, and thereby distend the elastic abdominal 

 wall and compress the gases contained in the intestines. Thus, 

 the diaphragmatic movements cause a rhythmical heaving of the 

 abdomen. Respiration depending chiefly on the action of this 

 one muscle, is, therefore, spoken of as abdominal respiration. On 

 the other hand, when the ribs are the chief cause of expansion of 

 the upper parts of the chest, it is called thoracic or costal respiration. 



These two types of respiratory movements may be imitated 

 voluntarily, and are variously combined in different individuals 



