DIAPHRAGM. 



broad digitation into the point of the bone and 

 into about one half of the adjoining portion of 

 its cartilage. The next fibres are still longer, 

 usually the longest of all ; they run outwards, 

 then downwards, forming the second digitation, 

 which is attached in a similar manner to the 

 eighth rib. The following fibres becoming 

 shorter as they approach the spinal notch, go to 

 the ninth and tenth ribs, and are similarly con- 

 nected. The succeeding ones, still shorter, 

 proceed to the eleventh and twelfth, and attach 

 themselves to a considerable portion of their 

 length. In the two lowest intercostal spaces 

 the diaphragm and transversus abdominis are 

 united by a common aponeurosis, which is very 

 thin ; and here it is not very unusual to meet 

 with a deficiency in the diaphragm. The thin 

 portion of the muscle, near to the cmra, has its 

 short fleshy fibres inserted into the ligamentum 

 arcuatum externum.* ( Fig. 1, d.} This last appel- 

 lation is bestowed on a thin aponeurosis which 

 stretches from the inferior margin of the last rib 

 to the point of the transverse process of the first 

 lumbar vertebra. In reality it is nothing more 

 than the anterior layer of the tendon of the 

 transversus abdominis which lies in front of the 

 quadratus lumborum muscle, and is connected 

 to the lowest rib. By pulling the rib outwards 

 the aponeurosis is projected into a fold which 

 looks like a ligament. It is designated ex- 

 ternum to distinguish it from another that is 

 much stronger and more truly ligamentous, 

 which arches over the psoas magnus muscle, 

 is attached to the transverse process of the 

 first lumbar vertebra (just where the former 

 ends), and to the body of the second. The 

 latter is known as the ligamentum arcuatum 

 internum f (fig- 1,/;) it is also called the true, 

 and the external thej'alse, names derived from 

 their structure. 



The vertebral or smaller muscle of the dia- 

 phragm is placed almost perpendicularly. The 

 fibres pass oft' from the concave margin of the 

 tendon which is turned to the spine. They run 

 downwards and a little backwards at first, then 

 along the lumbar vertebrae, into which they are 

 principally inserted. The shortest and most 

 external of them go to the internal ligamentum 

 arcuatum; but the greater number form two 

 large and long fasciculi, the crura, or pillars, or 

 appendices of the diaphragm. 



The right crus is longer and thicker than the 

 left, and is nearer to the middle line. It is 

 attached by tendinous slips to the bodies of the 

 three (often of the four) superior lumbar ver- 

 tebrae and to the intervertebral substances. The 

 left is attached in a similar way, but never de- 

 scends so low. Both become smaller as they 

 pass down, the more external fibres being 

 soonest inserted. The muscular bundles, on 

 quitting the cordiform tendon, separate imme- 

 diately from each other, to permit the oesopha- 

 gus to pass into the abdomen, and unite asain 

 behind that tube. Here a crossing or inter- 

 lacing of the fibres takes place, a considerable 

 bundle descending from the left side of the 



* Arcus tendineus exterior, Senac. 

 t Arcus tendineus interior, Id. 



oesophagus to the fight crus, and a smaller one 

 from the right side to the left crus. In general 

 the latter is placed anteriorly ; and occasionally 

 two bundles descend from each side alternating 

 with their opposites. The fleshy fibres again 

 separate on a level with the lower edge of the 

 last dorsal vertebra to allow the aorta to pass, 

 and they continue afterwards distinct. 



The foramina or openings which present 

 themselves in this septum require to be noticed. 

 Three large ones have been already mentioned ; 

 but as the organs which they transmit are of 

 great importance, they deserve more minute at- 

 tention. The first is situated in the tendon of 

 the diaphragm, toward its posterior part, a little 

 to the right of the centre (fig.\, c). It corre- 

 sponds to the line of division between the middle 

 and right lobes. Its shape is quadrangular, 

 (foramen quadratumj) having an anterior, a pos- 

 terior, a right and a left edge. The right is the 

 longest, the anterior the shortest, and these two 

 often appear to form but one. The inferior 

 vena cava passes through this opening and im- 

 mediately empties itself into the right auricle of 

 the heart. The vein is firmly connected to the 

 foramen by means of thin aponeuroses sent off 

 from the tendinous margins; the posterior 

 margin sending fibres upwards, the lateral 

 downwards, and the anterior in both directions. 

 This is the highest opening in the diaphragm, 

 being on a level with the lower edge of the 

 ninth dorsal vertebra and fifth rib. As the 

 boundaries of it are entirely tendinous they 

 cannot act on the vein themselves, and the ac- 

 tion of the muscular fibres only serves to keep 

 it dilated. Some branches of the phrenic nerve 

 accompany this vein. 



A little to the left of the median line, and 

 close behind the central tendon, we find an 

 opening of an elliptical form through which the 

 oesophagus and pneumogastric nerves pass (Jig. 

 1, e). Its major axis, two inches in length, is di- 

 rected obliquely dowr wards and backwards. The 

 borders are entirely muscular, at least very ge- 

 nerally, for it sometimes happens that the ante- 

 rior extremity is bounded by the cordiform ten- 

 don. It results from a separation of the fibres 

 which are descending to constitute the crura, 

 and may be said to lie between the crura. The 

 crossing or interlacing of the fibres which takes 

 place just behind it must enable them to shut 

 up this opening completely when they act 

 strongly. This foramen is on a level with the 

 tenth dorsal vertebra, its upper and lower an- 

 gles corresponding to the planes of the upper 

 and lower surfaces of that bone. 



About two inches below the inferior point 

 of the oesophageal opening the aorta may be 

 seen, coming out of the thorax, opposite the 

 lower edge of the last dorsal vertebra (Jig. 1, a.) 

 This great vessel enters the abdomen by a canal 

 which is formed posteriorly by bone, anteriorly 

 by the decussating fibres, and on either side by 

 the crura of the diaphragm. These crura, after 

 passing along the sides of the artery, almost 

 meet behind it by their tendinous expansions 

 lower down. The margin of the aortic opening 

 is bordered with tendon, and the fleshy fibres 

 are so connected with it that their action does 



B 2 



