nut at all diminish the size of the p;* 

 Along with the aorta and to its right side we 

 Me the vena azygos and thoracic duct passing 

 into the tliorax. 



Some other foramina transmit vessels and 

 nerves, but they are very small and irregular. 

 The sympathetic nerve usually passes with the 

 psoas muscle under the internal li^amentum 

 arcuatum. The riuht splanchnic slips out of 

 the thoiax between the fibres of tlie right eras, 

 at a point internal, superior, and anterior to the 

 sympathetic. The left splanchnic comes in the 

 same way, or more frequently with the aorta. 

 The lesser splanchnic passes at the outer side 

 of the former, separated from it by a few fibres. 

 Behind the external ligamentum arcuatum the 

 last dorsal nerve may be seen. Filaments of 

 the phrenic nerve pierce the muscle in several 

 places, principally its tendinous part, and some 

 pass through the opening for the vena cava. 

 And branches of the internal mammary artery 

 creep through those cellular spaces which are 

 left between the xiphoid cartilage and first 

 costal attachment. 



The ti]t]tcr muse If of the diaphragm is lined 

 for the most part of its under surface by the 

 peritoneum, and on its upper by the pleurae 

 and pericardium ; being thus placed between 

 serous membranes. In some points the peri- 

 lonfiim is reflected off to form ligaments for 

 the liver, and there this last organ comes in 

 contact with the muscle. The same thing oc- 

 curs to a small extent in the case of the kid- 

 neys. The upper surface too is for a little way 

 all along its margin destitute of serous covering, 

 and in contact with the ribs, intercostal mus- 

 cles, quadratus lumborum, psoas, and triangu- 

 laris sterni. Over the serous membranes on 

 the thoracic surface we find on each side the 

 base of the lungs, and in the centre the heart 

 resting on the middle lobe of the tendon and 

 on some muscular fibres to Us right. The ab- 

 dominal surface is related to the liver, stomach, 

 spleen, and kidneys. 



The inferior muscle of the diaphragm has 

 one surface turned back to the spinal column, 

 and in contact with it and with a little of the 

 aorta; the other surface looks forwards, and is 

 covered by the suprarenal capsules, the semi- 

 lunar ganglia, and various nerves, the aorta and 

 its principal branches, the ascending cava, the 

 commencement of the abdominal vena porta 

 and its tributaries, the pancreas, stomach, duo- 

 licnum, and occasionally other parts. Little 

 or no peritoneum can touch this portion. 



Arteries. A muscle of so much importance 

 in the animal economy as the diaphragm, and 

 so perpetually in action, requires a large supply 

 of blood. This it receives through numerous 

 channels and from distinct sources ; and as all 

 its vessels inosculate freely in its substance, no 

 failure in the supply can well occur. The 

 phrenic and internal mammary are distributed 

 In Us middle; the same vessels, with the in- 

 tercostal, the lumbal, and some small aortic 

 t^i'js, feed the circumference. 



1'i-his. The veins of the diaphragm accom- 

 tbe arteriei as in other parts of the body; 

 ili-ry having one or two ven comites. 



DIAPHRAGM. 



The principal veins, however, correspond to the 

 phrenic artery, and pour their blood into two 

 trunks, a riyht and a left, which empty them- 

 selves into the cava. They are usually seen 

 on the under surface of the tendon, sometimes 

 on the upper ; or there may be two above and 

 l\u> In-low. Occasionally they lie between the 

 two surfaces, so that their entrance into the 

 cava is not seen ; and in some cases they join 

 the hepatic veins. 



Lymphatics. The diaphragm is furnished 

 with lymphatic vessels as other muscles, but 

 there is nothing peculiar in them. They are 

 not easily demonstrated, as they do not form 

 any very distinct trunks, but join with the 

 lymphatics of the neighbouring organs. 



Nerves. The diaphragm receives a great 

 number of nerves. The lumbar send twigs to 

 the crura, the lower dorsal to the broad muscle, 

 and there is a phrenic plexus sent off from the 

 solar, which accompanies the phrenic arteries, 

 and distributes its numerous and delicate fila- 

 ments with extreme minuteness to the under 

 surface of the muscle. From the plexus which 

 the eighth pair forms on the stomach, we trace 

 also some fine filaments. But the chief and 

 most important nerves are the phrenic. The 

 phrenic nerve arises from the cervical plexus ; 

 its principal origin is from the fourth cervical 

 nerve, to which there is usually joined a small 

 twig from the third. It runs down along the 

 anterior scalenus, and gets into the thorax be- 

 tween the subclavian artery and vein. In the 

 neck it generally receives filaments from each 

 cervical nerve. As it enters the thorax, it com- 

 municates with the inferior cervical ganglion, 

 and gets a filament from the descendens noni 

 and the pneumogastric. The nerve thus formed 

 is conducted by the mediastinum and pericar- 

 dium, in front of the root of the lung, to the 

 diaphragm ; the left being a little longer than 

 the right, and thrown somewhat further back 

 by the position of the heart. 



It enters the diaphragm at the anterior edge 

 of the tendon in six or seven branches, the 

 largest of which pass backwards. Some go 

 through the muscle, ramify on its under sur- 

 face, and anastomose with the solar plexus ; 

 and one may usually be traced through the 

 opening for the cava on to that plexus. The 

 influence which these nerves exert on the organ 

 will presently be adverted to. 



Uses. The chief use of the diaphragm is to 

 assist in the function of respiration, and it will 

 be found to be the principal agent in the me- 

 chanical part of that process. By its action 

 the thoracic cavity is enlarged from above 

 downwards, whilst its circumference is in- 

 creased by the intercostal and other muscles. 



When the diaphragm acts, the entire muscle 

 descends, pushing the abdominal viscera down- 

 wards and forwards ; but its different portions 

 descend very unequally. The tendinous centre 

 is nearly fixed, and the crura are incapable of 

 much change of position ; it is only in the 

 broad lateral expansions that the motion is very 

 apparent. The muscular fibres of these when 

 relaxed are pressed upwards, and present 

 arches, convex to the thorax, and rising even 



