RESPIRATION. 



383 



three, which are almost horizontal. 

 The general arrangement and appearance 

 of the thorax are shown in Fig. 185. 



The costo-vertebral and costo-chon- 

 dral and the chondro-sternal articulations 

 are diarthrodial in character and endow 

 the thoracic walls with a considerable 

 degree of mobility. The costo-vertebral 

 joints are two in number, the first being 

 formed by the beveled head of the rib 

 and the bodies of the two adjoining ver- 

 tebrae; the second, by the tubercle of the 

 rib and the transverse process. The 

 costo-chondral and the chondro-sternal 

 articulations, as their names imply, are 

 formed by the ribs, cartilages, and 

 sternum. 



The muscles which complete the 

 formation of the thoracic walls are as 

 follows: the diaphragm, the intercostales 

 externi and interni, the levatores costa- 

 rum, the triangularis sterni, and the 

 infra-costales. 



The diaphragm is the musculo-mem- 

 branous sheet which closes the inferior 



13 



FIG. 1 86. DIAPHRAGM, INFERIOR ASPECT, i. Anterior 

 and middle leaflet of central tendon. 2. Right leaflet. 3. 

 Left leaflet. 4. Right crus. 5. Left crus. 6, 6. Intervals 

 for phrenic nerves. 7. Muscular fibers, from which the 

 ligamenta arcuata originate. 8. Muscular fibers that arise 

 from the 1 inner surface of the six lower ribs. 9. Fibers 

 that arise from ensiform cartilage. 10. Opening for inferior 

 vena cava. n. Opening for esophagus. 12. Aortic open- 

 ing. 13, 13. Upper portion of transversalis abdominis, 

 turned upward and outward. 14. Anterior leaflet of trans- 

 versalis aponeurosis. 15, 15. Quadratus lumborum. 16, 

 1 6. Psoas magnus. 17. Third lumbar vertebra. 



FIG. 185. THORAX, ANTERIOR VIEW. 

 i. Manubrium sterni. 2. Gladiolus. 3. 

 Ensiform cartilage of xiphoid appendix. 

 4. Circumference of apex of thorax. 5. 

 Circumference of base. 6. First rib. 

 7. Second rib. 8, 8. Third, fourth, 

 fifth, sixth, and seventh ribs. 9. Eighth, 

 ninth, and tenth ribs. 10. Eleventh and 

 twelfth ribs, n, n. Costal cartilages. 



opening of the thorax 

 and completely sepa- 

 rates its cavity from that 

 of the abdomen. It con- 

 sists of two muscles 

 which arise from the 

 bodies of the first three 

 or four lumbar verte- 

 brae and neighboring 

 fascia, from the border 

 of the six lower ribs, and 

 from the ensiform car- 

 tilage (Fig. 186). From 

 this extensive origin the 

 muscle-fibers pass cen- 

 trally to be inserted into 

 a common tendon. As 

 the direction of the fibers 

 is from below upward 

 and inward, the dia- 

 phragm is somewhat 

 dome shaped. Its infe- 

 rior border is for a short 

 distance in contact with 

 the sides of the thorax. 



