1897 Journal of the American Medical Association  
The diaphragm is the chief characteristic of mammalian myology. The amphibia and animals below them in scale of structure have no diaphragm. The first distinct trace of it may be found in crocodile and bird, where the muscular fibers which are concerned in its formation arise from ribs. Even animals as high in the ascending scale as birds have an imperfect diaphragm; it does not separate the lungs and abdomen of aves completely. In fact several descriptions have appeared as to what is
more » ... o what is considered a diaphragm in birds. A complete diaphragm which arises from the vertebral column, ribs and sternum is a mammalian property only. The exact mode of the formation of the muscle is not fully known. The mammalian diaphragm is probably homologous to the so-called diaphragm of other vertebrates. The mammalian diaphragm is supplied by the phrenic nerves, which arise from the fourth, fifth and sixth cervical nerves and course along the lateral borders of the heart in contact with the pericardium to supply chiefly the anterior primitive portion of the diaphragm. In the human species it receives a sympathetic branch from the inferior cervical ganglion. Some of the lower intercostal nerves pass to the midriff. Besides, the diaphragm receives sympathetic branches from the abdominal brain along the phrenic arteries-the phrenic plexus. Originally the body cavity extended in the embryo from the visceral arches to the pelvic cavity; in the mammalian embryo the pericardiothoracic cavity begins to be distinctly marked off from the future abdominal cavity by a transverse fold. This transverse fold begins at the vertebral and lateral wall, projects median-ward and dorsal-ward into the primitive pleuro-peritoneal cavity. This folds marks the course which the terminal part of the omphalomesenteric vein takes in order to reach the heart. Oscar Hertwig says, " subsequently there is found imbedded in the transverse fold all of the venous trunks which empty into the arterial sinus of the heart, i.e., the omphalo-mesenteric and umbilical vein with the ducts of Cuvier which collect the blood from the walls of the trunk." From this view it would result that the transverse fold-the incipient diaphragm-is intimately connected with the development of the veins. Similar folds are produced in the peritoneum by blood vessels as the plica-duodeno-jejunalis, the folds due to the arterias hypogastrics and umbilical vein. It is known as the septum transversum or as Uskow named it, " massa transversum." The primary diaphragm really belongs to the heart, as it consisted originally of projecting folds through which were conducted blood vessels to the great fluid or blood center-the heart. It may be noticed that the ventral part, i.e , the primitive or original part, of the diaphragm is the older and this explains why the two phrenic nerves chiefly supply the primitive or anterior portion. The muscular portion of the diaphragm gradually projects from the lateral and dorsal.aspects toward the central portion of the body cavity between the growing liver and sinus venosus. A final fusion results between the primitive and secondary portion of the diaphragm. The hepatic and diaphragmatic development is inseparably connected early in embryonic life. But first the pericardial cavity is completely closed and then there remains two tubular cavities projecting from the peritoneal cavity bilaterally up to the visceral clefts. His called these cavities, thoracic prolongations of the abdominal cavity-a very suitable name. Into these original peritoneal prolongations juts out the lung structures, growing from the vertebral wall of the intestinal tube. Later in embryonic life the pericardial cavity is closed and occupies the chief ventral side of the embryo, the thoracic cavities now closed occupy the dorsal side, while the rapidly growing peritoneal cavity occupies the posterior portion of the embryo, all three cavities Fig. 1. -Diagram to illustrate tie lymphatic drainage of the centrum tendineum of the diaphragm into the .two anterior and two posterior trunks. D, D, upper and lower end of the thoracic duct; 1, outer end of the dinphragm; 2, anterior lymph trunks passing on the posterior surface of the xyphoid appendix to accompany the mammary arteries; 3.8, two posterior trunks of lymphatic vessels which dra n the centrum tendineum and empty into the thoracic duct; 5,5. valves of the trunks; 6, 7, 8, are dilated lymph spaces in the tendon. The black spot represents the point of the centrum tendineum where the heart rests on it, at which point there are no lymph spaces; 9 represents the mouths of the two anterior channels. distinctly divided off by the characteristic mammalian muscle of the diaphragm. The pericardial sac first closes from above by the forward projection of the ducts of Cuvier, the primitive diaphragm forming the lower portion of the pericardial sac. Finally the edges of the projecting folds, due to the ducts of Cuvier, fuse and the pericardial sac is formed. The remains of Cuvier's ducts is the superior vena cava. From the dorsal and lateral walls of the trunk project folds, known as the pillars of Uskow, which fuse with the original septum transversum which was thrown into a fold by the veins which course to empty their contents into the heart. The diaphragm has an older ventral part supplied by the phrenic nerves and a younger dorsal part. The pericardial sac is of enormous size in the embryo while the two narrow, lateral tubular sacs hold the rudimentary lungs which are very small from non-use and slight blood supply. But with further ventral growth of the lungs they detach more and more the wall of the pericardium from the diaphragm and from the lateral walls of the thoracic cavity, thus increasing the pleural diaphrag-Downloaded From: by a University of Arizona Health Sciences Library User on 06/08/2015
doi:10.1001/jama.1897.02440050011001b fatcat:r3xipff5rrcddab3lailbbvrmi