194 MYOLOGY, OR ANATOMY OF MUSCULAR SYSTEM 



to similar muscles of the male, the sphincter vaginas to the 

 bulbocavernosi. The constrictor urethras is the transversus 

 perinei profundus, and differs from that of the male by being 

 divided into lateral halves by the vagina. 



The Diaphragm (Midriff) 



A partition between the abdomen and thorax, rising by 

 muscular fibers as vertebral, costal, and sternal portions. 



The crura, or pillars of the vertebral portion, connected with 

 the anterior common ligament, rise from the bodies and inter- 

 vertebral substance of the lumbar vertebrae, the right from 

 the second, third, and fourth, the left from the second and 

 third; they arch over the aorta from right to left, and meet 

 behind it from left to right. The muscular fibers from them 

 form a figure 8, leaving an opening for the esophagus. The 

 internal arcuate Ugament passes over the psoas muscle from 

 the outer side of the first lumbar body to the second trans- 

 verse process. The external arcuate ligament passes over the 

 quadratus lumborum from the second transverse process to 

 the last rib; they are the upper margins of fascia covering 

 those muscles; an arched ligament may pass over both muscles; 

 muscular fibers of the diaphragm rise from both. 



The costal portion rises from the lower six cartilages, inter- 

 digitating with the transversalis abdominis. The sternal 

 portion is very short a single muscular slip, sometimes two, 

 from the ensiform cartilage. 



The central tendon, trefoil, forms the highest part, convex 

 above, concave below; has three lobes, the right being the 

 largest, the left the smallest; the tendinous fibers are inter- 

 woven in every direction. 



There are three foramina: The hiatus aoriicus, in front of 

 the first lumbar, transmitting the aorta, thoracic duct, and 

 vena azygos magnus; the foramen for the esophagus, opposite 

 the tenth dorsal vertebra, entirely surrounded by muscle, 

 oval, transmits the esophagus, pneumogastric nerves, and 

 branches of the coronary artery; the foramen quadratum for 

 the vena cava is in the highest part of the central tendon, at 

 the level of the disk between the eighth and ninth dorsal ver- 

 tebrae; its sides are firmly attached to the vein. A sterno- 

 diaphragmatic ligament passes to this foramen. 



