DIAPHRAGM

n. Di'a3-fra2m. Gr., SiaQpayna. Lat., diaphragm a. Fr., diaphragme. Ger., Zwerchfell (1st def.), Zwerchmuskel (1st def.), Blendung (3d def.). It., diaframma. Sp., diafragma. In general, a partition or septum which more or le completely separates one cavity from another. 1. The musculi-tendinous partition between the thoracic and abdominal cavities. It ia situated at about the junction of the middle third with the upper third of the trunk, is somewhat elliptical in shape, its shortest diameter being the antero-posterior, and is arched, the concavity being directed downward. It is attached to the ensiform cartilage, the inner surfaces of the lower six or seven ribs, and their cartilages on each side, and to the ligament a arcuata externum and internum. It consists of a central aponeurotic expansion, the cordiform tendon, toward which the muscular fibres converge and with which they are blended. By its contraction the capacity of the thoracic cavity is increased. [L, 31, 142, 172.] Cf. LIG AMENTUM arcuatum externum, PILLARS of the d., and Cordiform TENDON. 2. In conchology, a THE DIAPHRAGM. a, the ens i'orm cart i'agu; fi, the central tendon; f, the opening for the oesophagus; d, the left leaflet; >, the opening Cor the aorta; /, the left cms; g, psoas magnus; h, trnnsversalis; i, quadratus lumborum; k, llgamentum arcuatum externum; /, lig amentum arcuatum internum; m, the right leaflet; n, the opening for the vena cava; o, the middle leaflet; p, the right cru a, straight calcareous plate dividing the cavity of a shell into two parts. [L, 180.] 3. Of a microscope, a perforated partition, usually in the form of a circular plate pivoted at its centre to the stage and having a number of circular perforations of various sizes so arranged that, by turning the plate on its pivot, the centre of any one of them may be made to coincide with the central axis of the instrument; used to regulate the amount of light admitted to the O, no; O", not; O, whole; Th, ihin; Tli, the; U, like oo in too; [s. 553]