442. CHAPTER VII. THE DIAPHRAGM.
HEISTER. "The diaphragm is a large, robust, muscular skin, transversely dividing the abdomen from the thorax, and hence called by the Latins, septum transversum. It is situated obliquely, between the abdomen and the thorax; in such a manner, that the anterior and right portion is the higher, while the posterior portion inclines considerably more downwards. Its superior surface is convex; its inferior surface, concave. It is connected with the sternum, the false ribs, the pericardium, the mediastinum, and the lumbar vertebrae. Its figure is commonly compared with that of a racket basket, or of the fish termed ray or thornback; but transversely it is very oblong and elliptical. It has in it two large openings; one on the left side, for the transmission of the esophagus and par vagum; the other on the right side, for the transmission of the inferior vena cave: and an interstice between the two heads of the inferior portion [lesser muscle], transmitting the aorta, the vena azygos, and the thoracic duct. Its vessels are termed the phrenic, from the Greek [scanner unable to insert symbols], signifying the diaphragm. Its arteries arise,
1. From the aorta or the coeliac artery.
2. From the subclavian or mammary arteries.
3. From the intercostal and lumbar arteries. Its veins run to the cave, the vena azygos, and the subclavian vein.
Its nerves are:
1. The two great phrenic nerves, arising on each side from the vertebral nerves of the neck, and which are almost exclusively inserted into the diaphragm.
2. Small branches from each intercostal nerve and from the par vagum.
Its lymphatics run to the jugular vein. The diaphragm is covered with a membrane, derived on the upper side from the pleura, on the lower side from the peritonaeum. Its main body is muscular, of which the superior portion, large and elliptical, arises from the false ribs, from the transverse muscles of the abdomen, and from the xiphoid cartilage; and by its tendon, produces the nervous centre [centrum nervosum] of the diaphragm, of a nearly triangular figure: the inferior portion has two origins, namely, from the lumbar vertebrae on each side, and is inserted almost into the centre of the superior portion. (Comp. Anat., n. 257.) Tab. iii., fig. 13, exhibits the diaphragm viewed from below;...its superior muscle arising by thick fleshy fibres from the sternum and the cartilages of the ribs; which fibres all run towards the tendinous part, like radii to a centre: the inferior muscle, which is in a manner double: the tendinous part, or tendinous centre, to which the pericardium adheres superiorly, and the tendinous fibres of which, as Santorinus observes, decussate and wonderfully interweave with one another for the sake of strength: the transverse elliptical foremen in the tendinous part, through which the inferior vena cava passes: the oblong foramen in the fleshy part, through which the esophagus makes it way to the stomach: the space or interstice between the two heads of the inferior muscle, where the aorta descends from the thorax into the abdomen; and the thoracic duct, and frequently the vena azygos, ascend from the abdomen into the thorax: also a fleshy portion that existed in this subject in the tendinous portion: lastly, two muscular appendages, which are of a very various shape in different subjects, and are sometimes present and sometimes not. (Comp. Anat., expl. tab. iii., fig. 13.) The uses of the diaphragm, are,
1. To assist in respiration; for it is pressed downwards in inspiration, but upwards, into the cavity of the thorax, in expiration.
2. To further the motions of the contents of the abdomen, namely, of the stomach, the intestines, the liver, the spleen, and of the chyle, the bile, and c.
3. To assist in the expulsion of the faeces and urine, and during parturition, of the foetus, the secunaines, and c.
4. In addition to the above, it also transmits the intercostal nerves." (Comp. Anat., n. 257.)
