DIAPHRAGM. 369 



being from side to side, somewhat fan-shaped, the broad elliptical portion being 

 horizontal, the narrow part, which represents the handle of the fan, vertical, and 

 joined at right angles to the former. It is from this circumstance that some an- 

 atomists describe it as consisting of two portions, the upper or great muscle of 

 the Diaphragm, and the lower or lesser muscle. It arises from the whole of the 

 internal circumference of the thorax, being attached, in front, by fleshy fibres 

 to the ensiform cartilage ; on either side, to the inner surface of the cartilages 

 and bony portions of the six or seven inferior ribs, interdigitating with the 

 Transversalis ; and behind, to two aponeurotic arches, named the ligamentum 

 arcuatum externum and internum, and to the lumbar vertebrae. The fibres from 

 these sources vary in length ; those arising from the ensiform appendix are very 

 short and occasionally aponeurotic ; those from the ligamenta arcuata, and more 

 especially those from the ribs at the side of the chest, are longer, describe well- 

 marked curves as they ascend, and finally converge to be inserted into the cir- 

 cumference of the central tendon. Between the sides of the muscular slip from 

 the ensiform appendix and the cartilages of the adjoining ribs, the fibres of the 

 Diaphragm are deficient, the interval being filled by areolar tissue, covered on 

 the thoracic side by the pleuraa ; on the abdomini, by the peritoneum. This is, 

 consequently, a weak point, and a portion of the contents of the abdomen may 

 protude into the chest, forming phrenic or diaphragmatic hernia, or a collection 

 of pus in the mediastinum may descend through it, so as to point at the epi- 

 gastrium. 



The ligamentum arcuatum internum, is a tendinous arch, thrown across the 

 upper part of the Psoas Magnus muscle, on each side of the spine. It is con- 

 nected, by one end, to the outer side of the body of the first, and occasionally 

 the second lumbar vertebra, being continuous with the outer side of the tendon 

 of the corresponding crus ; and, by the other end, to the front of the transverse 

 process of the second lumbar vertebra. 



The ligamentum arcuatum externum is the thickened upper margin of the 

 anterior lamella of the transversalis fascia ; it arches across the upper part of 

 the Quadratus Lumborum, being attached, bv one extremity, to the front of the 

 transverse process of the second lumbar vertebra ; and, by the other, to the 

 apex and lower margin of the last rib. 



To the spine, the Diaphragm is connected by two crura, which are situated 

 on the bodies of the lumbar vertebrae, one on each side of the aorta. The 

 crura, at their origin, are tendinous in structure ; the right crus, larger and 

 longer than the left, arising from the anterior surface of the bodies and inter- 

 vertebral substances of the second, third, and fourth lumbar vertebras ; the left, 

 from the second and third ; both blending with the anterior common ligament 

 of the spine. A tendinous arch is thrown across the front of the vertebral 

 column, from the tendon of one crus to that of the other, beneath which passes 

 the aorta, vena azygos major, and thoracic duct. The tendons terminate in two 

 large fleshy bellies, which, with the tendinous portions above alluded to, are 

 called the crura, or pillars of the Diaphragm. The outer fasciculi of the two 

 crura are directed upwards and outwards to the central tendon ; but the inner 

 fasciculi decussate in front of the aorta, and then diverge, so as to surround 

 the oesophagus before ending in the central tendon. The anterior and larger 

 of these fasciculi is formed by the right crus. 



The Central or Cordiform Tendon of the Diaphragm is a thin tendinous apo- 

 neurosis, situated at the centre of the vault formed by the muscle, immediately 

 beneath the pericardium, with which its circumference is blended. It is shaped 

 somewhat like a trefoil leaf, consisting of three divisions, or leaflets, separated 

 from one another by slight indentations. The right leaflet is the largest ; the 

 middle one, directed towards the ensiform cartilage, the next in size; and the 

 left, the smallest. In structure, the tendon is composed of several planes of 

 fibres, which intersect one another at various angles, and unite into straight or 

 curved bundles, an arrangement which affords it additional strength. 

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