Volume 2

The cyclopaedia of anatomy and physiology / edited by Robert B. Todd.

Date:
1836-1859
Catalogue details

Licence: Public Domain Mark

Credit: The cyclopaedia of anatomy and physiology / edited by Robert B. Todd. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    CYCLOPAEDIA ANATOMY AND PHYSIOLOGY. DIAPHRAGM (in anatomy), (Jia^ay^a, inter, and (p^curo-a, sepio, claudo ; Lat. dia- phragm a ; Ital. diaf'ramma; Fr. diaphragms; Ger. Zwerchfell; Eng. midriff), the name given to that musculo-tendinous septum by which the cavities of the thorax and abdomen 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 muscularagentin the Mammalia, respiration, being effected by the skin, intestines, stigmata, trachea1, 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.} 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 cor facile princeps, 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. B