806 



SPECIAL PHYSIOLOGY. 



114. 



liquely attached ribs; for by such a movement, as may be illustrated 

 on the skeleton, or on an apparatus consisting of pieces of hoops at- 

 tached obliquely to a common upright 

 support, the ribs, in becoming more 

 horizontal, are not merely lifted, but 

 slightly rotated on their hinder at- 

 tached extremities; their sides are 

 thus carried outwards, their outer 

 surfaces being turned somewhat up- 

 wards, and their inner surfaces down- 

 wards. The total result, as it affects 

 all the ribs, is to expand the thorax 

 in its transverse diameter. Lastly, 

 the increase in the vertical diameter 

 or height of the thorax, which, in its 

 costal portion, is diminished by the 

 antero-posterior and transverse ex- 

 pansion, is accomplished by the action 

 of the arched or vaulted diaphragm, 

 Fig. 114, d, which forms the base of 

 the thorax. The central tendinous 

 expansion, the diaphragm, is drawn 

 down by the contraction of its circum- 

 ferential muscular parts ; and this 

 movement, named the descent of the 

 diaphragm, causes an important elon- 

 gation of the thoracic space. 



Of these three modes of enlarge- 

 ment of the thoracic cavity, its elon- 

 gation from above downwards, by the 

 descent of the diaphragm, is by far 

 the most considerable. In ordinary 

 respiration, it constitutes in men, and, 

 it is said, particularly in children, the 

 principal respiratory movement; but 

 it is accompanied by a slight lifting of 

 the walls of the thorax, in front, at 

 the sides, and especially at the lower 

 p art O f tne c hest. When the dia- 

 phragm thus descends, the abdominal 

 viscera do so likewise, and the abdominal walls, their muscles proba- 

 bly relaxing, become prominent ; whilst in expiration, when, as may 

 be supposed, the diaphragm ascends, the abdominal viscera are carried 

 upwards, and the abdominal walls, slightly reacting, fall in. Hence, 

 respiration performed, chiefly or entirely, by means of the diaphragm, 

 is termed abdominal, diaphragmatic, or inferior costal respiration ; it 

 is the typical form of respiration in the male and in children. When 

 breathing is mainly performed by the movements of the ribs, it is 

 termed pectoral or superior costal respiration, and this is the charac- 

 teristic form of breathing in the female, a fact which has been, by 



Fig. 114. Diagrammatic view of an antero- 

 posterior section of the cavities of the thorax 

 and abdomen, with the diaphragm interven- 

 ing, to show the changes in the position of 

 this septum, and of the walls of the chest and 

 abdomen, in respiration ; a, abdominal cavity ; 

 t, thorax ; v, v, vertebral column ; d, dia- 

 phragm. The dark lines show the position of 

 the parts after inspiration, the dotted lines 

 after expiration. , section of the sacrum, 

 and p, of the sympnysis pubis, forming the 

 posterior and anterior boundaries of the pelvic 

 cavity, which communicates above with the 

 abdomen. 



