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ANATOMY AND PHYSIOLOGY 



DIAPHRAGM (in anatomy), (& 

 3ta, inter, and (pgaoTu, sepio, claudo ; Lat. dia- 

 phrugma ; Ital. diuframma ; Fr. diaphragme ; 

 Ger. Zwerchfell; Eng. midriff), the name given 

 to that musculo-tendmous septum by which the 

 cavities of the thorax ancTabdomen are separated 

 from each other in the Mammalia. 



Nothing analogous to the diaphragm of mam- 

 mals can be detected in the Invertebrate classes 

 of animals ; the function of which it is a princi- 

 pal muscular agent in the Mammalia, respiration, 

 being effected "by the skin, intestines, stigmata, 

 tracheae, gills, &c. Most of the Vertebrata, 

 however, exhibit something analogous to the 

 diaphragm. Thus in Fishes the muscular sep- 

 tum dividing the cavity of the branchial ap- 

 paratus (thorax) from the abdomen bears a 

 certain resemblance to the diaphragm. Birds 

 have muscles which proceed obliquely upwards 

 in the form of flat bundles of fibres from the 

 middle of the lower ribs to the under part of 

 the lungs, where they are lost in the pleura 

 covering these organs ; and thus by their con- 

 traction depress the lungs themselves, expand 

 their cells, and facilitate the ingress of air 

 into them. These muscular fibres are particu- 

 larly developed in the parrot.* But, as has 

 been said, it is only in Mammalia that the 

 genuine diaphragm is to be found ; and all the 

 animals of this class possess it. The organ, as 

 might be expected, undergoes some modifica- 

 tions in different families. In amphibious and 

 cetaceous mammalia it approximates to that of 

 birds. A very strong and fleshy diaphragm is 



* C. G. Carus, Comparative Anatomy. 

 VOL. II. 



attached to the dorsal side of the cavity of the 

 trunk so low down that it ascends considerably 

 in order to be connected in a peculiar manner 

 with the upper and anterior extremity of the 

 abdominal muscles ; so that the lungs lie be- 

 hind rather than above the diaphragm.* In 

 the porpoise there is no central tendon .f The 

 horse, elephant, rhinoceros, and other animals 

 whose ribs, approach the pelvis, have a very 

 extensive diaphragm, which forms an elevated 

 arch towards the thorax.J This shape is neces- 

 sary to accommodate the bulky contents of the 

 abdomen, without altering the attachments of 

 the muscle, which, as in man, are connected to 

 the lowest ribs. Some other variations from 

 the structure and form of the diaphragm in man 

 might be noticed, but they are very unim- 

 portant. We shall therefore proceed to give a 

 detailed account of the muscle in the human 

 subject. 



DIAPHRAGM (human anatomy). The dia- 

 phragm in man is a muscle of great importance 

 (post corjacileprincepsj Haller), being the chief 

 agent by which respiration is carried on, while 

 it assists in the performance of many other im- 

 portant processes. It is placed between the 

 thorax and abdomen, forming a. convex floor 

 to the former, and a concave ceiling to the 

 latter. Although a single muscle, and situated 

 in the median line, it is not symmetrical ; the 

 right side of it is more extensive than the left. 

 Symmetry, however, was not necessary in an 



* C. G. Cams, Comparative Anatomy. 



t Tyson. 



$ Cuvier, Anat. Comp. vol. iv. 



