THE. RIBS 45 



The posterior or vertebral extremity is the head, next to the 

 head is the neck, and the remaining bony portion is the shaft. 

 The inner surface of the shaft is marked by a groove at its lower 

 border (the costal groove) in which the intercostal nerves and ves- 

 sels run, being thus protected from external injury. 



FIG. 40. THE THORAX. 



i, 2, Manubrium and body of sternum; 3, 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. (Sappey.) 



The first seven are called "true ribs," being connected in front 

 with the sternum by their cartilages. The remaining five are 

 "false ribs"; the eighth, ninth and tenth are connected in front, each 

 to the one above; the eleventh and twelfth are not connected with 

 anything in front, and are called "floating ribs." 



Thoracic vertebrae. Twelve in number; described with the 

 bones of the spinal colum'n. 



