352 THE MUSCLES AND FASCIAE 



Internal intercostal muscles, and internal mammary vessels; behind, with the 

 pleura, pericardium, and anterior mediastinum. 



The Levatores Costarum (Fig. 214), twelve in number on each side, are small 

 tendinous and fleshy bundles which arise from the extremities of the transverse 

 processes of the seventh cervical and eleven upper dorsal vertebrae, and, passing 

 obliquely downward and outward, are inserted into the upper border of the rib 

 below them, between the tubercle and the angle. The Inferior levatores divide 

 into two fasciculi, one of which is inserted as above described; the other fasciculus 

 passes down to the second rib below its origin ; thus, each of the lower ribs re- 

 ceives fibres from the transverse processes of two vertebrae. 



Nerves. The muscles of this group are supplied by the intercostal nerves. 



The Diaphragm (dtd(f>f>ay/jia, a partition ivall] (Fig. 216) is a thin, musculo- 

 fibrous septum, consisting of muscular fibres externally, which arise from the cir- 

 cumference of the thoracic cavity and pass upward and inward to converge to a 

 central tendon. It is placed obliquely at the junction of the upper with the middle 

 third of the trunk, and, separating the thorax from the abdomen, forming the floor 

 of the former cavity and the roof of the latter. It is elliptical, its longest diameter 

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

 horizontal, the narrow part, the crura, which represents the handle of the fan, 

 vertical, and joined at right angles to the former. It is from this circumstance 

 that some anatomists 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 Trans- 

 versalis ; and behind, to two aponeurotic arches, named the ligamentum arcuatum 

 externum et internum, and by the crura, 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 cartilages of 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 circumference 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 pleurae ; on the abdominal, by the peritoneum. This is, 

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

 protrude 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 epigas- 

 trium. A triangular gap is sometimes seen between the fibres springing from the 

 internal and those arising from the external arcuate ligament. When it exists, the 

 kidney is separated from the pleura only by fatty and areolar tissue. 



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

 upper part of the Psoas rnagnus muscle, on each side of the spine. It is connected, 

 by one end, to the outer side of the body of the first or 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 first, and sometimes 

 also to that of the second, lumbar vertebra. 



The ligamentum arcuatum externum is the thickened upper margin of the 

 anterior lamella of the lumbar fascia ; it arches across the upper part of the Quad- 

 ratus lumborum, being attached, by one extremity, to the front of the transverse 

 process of the first lumbar vertebra, and, by the other, to the apex and lower 

 margin of the last rib. 



The Crura. The Diaphragm is connected to the spine by two crura or pillars, 

 which are situated on the bodies of the lumbar vertebrae, 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 three or four upper lumbar vertebrae ; the left, from 



