438 



THE MUSCULATURE 



the place of the stem being taken by the region occupied by the vertebral column, one leaflet 

 lying on each side of this and one in front. The ventral part is usually placed somewhat to the 

 left and is more or less completel}' fused with the left leaflet. Between the ventral and the right 

 leaflets there is a large opening through which passes the inferior vena cava, the foramen venae 

 cavae. The leaflets are fused in front and behind this. 



Fig. 393. — Ventral Coccygeal Muscles (After Eisler.) — 1. M. sacrococcygeus anterior. 

 2. M. coccj-geus. 3. M. piriformis. 4. M. obturator inter nus 5. Fascia iliaca, above the iho- 

 psoas. 6. Fibrocartilago intervertebralis lumbosacralis. 7. Ventral trunk of first sacral nerve. 

 8. Sacral plexus. 



The fleshy portion of the muscle is composed of fibre-bundles which pass at first nearly 

 vertically upward and then arch over to be attached to the margins of the central tendon. The 

 sternal portion of the muscle is the shortest. It is often separated from the costal portion by a 

 small space through which the superior epigastric vessels pass. 



Nerve-supply. — From the phrenic nerves, one of which arises on each side from the third to 

 the fifth cervical nerves. Each nerve penetrates the diaphragm lateral to the central tendon 

 and breaks up into an extensive plexus on the inferior surface of the muscle. Some of the lower 

 interco.stal nerves also contribute to the sensory innervation of the margin of the muscle and pos- 

 sibly also slightly to the motor innervation. The sympathetic nerves furnish fibres for the 

 blood-vessels. 



Adinn.—'Yo enlarge the thoracic cavity and thus cause inspiration. According to R. Fick, 

 however, the diaphragm })lays a loss inii)()rtant part in insi)irali()n than is usuallv assumed for 

 it. The middle part of the central tendon is united to the pericardium and through this to 

 the cervical fascia, and is, therefore, not very movable. In the contraction of the muscle it is 

 the dorsal and lateral portions which in the main are flattened. The diai)hragm aids in defeca- 

 tion, parturition and vomiting, by the pressure it exerts on the abdominal viscera. It also 

 acts as a constrictor of the fjc.sophagus. 



Relations. — Above lie the heart and the lungs; below lie the liver, stomach, duodenum, 

 pancreas, spleen, kidneys, and sujjrarenal bf)dics. 



V aria firms. — The sfcrnal portion of the muscle is frequently absent. Infrequently the 

 diaphragm is incomi)letcly developed dorsally on the left side. This condition is rarer on the 

 right side. The extent of tlu; various insertions of the (lia|)hragni shows considerable individual 

 differences. The vertebral i)or(ion of the muscle may be slightly fused with the psoas or with the 

 (luadratus lumborum. Some fusion of the ventral jjortion cjf the muscle with the transversus 



