THORAX. 



1081 



against the period of gestation, when the ab- 

 domen cannot allow of so free a descent of 

 the diaphragm. 



Fig. 713. 



Respiratory Movements. Male, Front view. 



Inspiration, broken line. Ordinary, continuous 

 line. Expiration, dotted line. 



The lateral movement of ordinary breathing 

 is too limited to be represented by a line of 

 varying thickness : the position is given by 

 the continuous line,^g.s. 713. and 714. 



Fig. 714. 



enlargement of the thoracic cavity in both 

 sexes is made by the ribs, and not by the 

 diaphragm, as is generally believed. It 

 appears very questionable whether the dia- 

 phragm is any thing more than flattened and 

 that without descending. 



Of the position of the diaphragm. It is 

 clear that all that space between the line 

 of ordinary breathing and deep inspiration 

 (Jig- 711.), below the ensiform cartilage, 

 where the two lines cut each other, may be 

 considered as just so much space deducted 

 from the abdominal cavity ; and therefore 

 the abdominal cavity, by deep breathing, is 

 just so much less than it was in the posi- 

 tion of ordinary breathing. Now, if the dia- 

 phragm descends at this moment, whilst the 

 abdominal parietes are being constringed on 

 all sides, what becomes of the abdominal vis- 

 cera? We know that in ordinary breathing 

 the abdomen advances because the diaphragm 

 descends, and recedes because the diaphragm 

 ascends. We may suppose the same accom- 

 modating movement between the diaphragm 

 and abdominal parietes, to take place in deep 

 breathing. There can be no doubt that the cir- 

 cumference of the thorax is increased, as shown 

 in D.Jig. 670., and that the diaphragm must 

 extend its borders, and consequently the arch 

 must be flattened ; but this may be without 

 descending. We see (Jig. 670.) that the sec- 

 tion of the thorax to the area of the diaphragm 

 is as 40 to 133 the concavity of the dia- 

 phragm is enough to admit of its circumfe- 

 rence expanding without its descending. 



Fig. 715. is a diagram of sections of the base 

 of the living chest in three stages, u is the chest 

 in ordinary : A, as in extreme expiration ; c, as 

 in extreme inspiration. In this case the vital ca- 

 pacity was 305 cubic inches, and the mobility 

 of the chest was 5 inches, a range by no means 

 common. The area of the chest varied 27 

 superficial inches between extreme inspiration 

 and expiration.* 



In the sitting posture the same relations 



Fis. 715. 



Respiratory Movements. Female. Front view. 



Inspiration, broken line. Ordinary, continuous 

 line. Expiration, dotted line. 



(/;) Deep inspiratory* In Jig. 711. the 

 dotted line shows this position, as when a 

 man is just ready to displace his vital ca- 

 pacity-volume. The sternum is protruded 

 and the abdomen is drawn in. This is the same 

 in the female (Jig. 712.), the dotted line is 

 most advanced over the sternum, while over 

 the abdomen it is drawn inwards. 



So much is the abdomen drawn in- 

 wards by deep inspiration, that the portion of 

 the continuous line (Jigs. 711, and 712.), 

 representing the ordinary breathing is (over the 

 abdominal region) external to the dotted line 

 of deep inspiration. Therefore the greatest 



Ordinary 



30 inches. 



Expiration 



Inspiration 



74 inches. 



101 inches. 



Sections of the base of thorax in the three stages of 

 respiration, in t/ie living subject. 



* This is the chest of Jig. 711. 



