RIBS TRUE AND FALSE. 



71 



Fig. 27.* 



broad in the middle, and somewhat narrower at each extremity. 

 It presents on each side six articular notches, for the lower half of 

 the second rib, the four next ribs, and the upper half of the seventh. 



The inferior piece, or ensiform cartilage (3), is the smallest of the 

 three, often merely cartilaginous, and very various in appearance, 

 being sometimes pointed, at other times broad and thin, and at 

 other times again, perforated by a round hole, or bifid. It presents 

 a notch at each side for the articulation of the lower half of the 

 cartilage of the seventh rib. 



JDevelopement. By a number of centres, varying from six to 

 fourteen. 



Articulations. With sixteen bones; viz. with the clavicle, and 

 with seven true ribs at each side. 



Attachment of Muscles. To nine pairs and one single muscle ; 

 viz. to the pectoralis major, sterno-mastoid, sterno-hyoid, sterno- 

 thyroid, triangularis sterni, aponeurosis of the obliquus externus, 

 internus, and transversalis muscles, rectus, and diaphragm. 



RIBS. The ribs are twelve in number at each side ; the seven 

 first are connected with the sternum, and hence named true ; the 

 remaining five are the false ribs ; 

 and the two last shorter than the 

 rest, and free at their extremi- 

 ties, are the floating ribs. The 

 ribs increase in length from the 

 first to the eighth, whence they 

 again diminish to the twelfth; 

 in breadth they diminish gra- 

 dually from the first to the last. 

 Each rib presents an external 

 and internal surface, a superior 

 and inferior border, and two 

 extremities ; it is curved to cor- 

 respond with the arch of the 

 thorax, and twisted upon itself, 

 so that when laid upon its side, 

 one end is tilted up, while the 

 other rests upon the surface. 



The external surface is con- 

 vex, and marked by the attach- 

 ment of muscles; the internal 



is flat, and corresponds with the pleura; the superior border is 

 rounded ; and the inferior sharp and grooved upon its inner side, 

 for the attachment of the intercostal muscles. Near its vertebral 



* An anterior view of the thorax. 1. The superior piece of the sternum. 2. The 

 middle piece. 3. The inferior piece, or ensiform cartilage. 4. The first dorsal 

 vertebra. 5. The last dorsal vertebra. 6. The first rib. 7. Its head. 8. Its neck, 

 resting against the transverse process of the first dorsal vertebra. 9. Its tuberosity. 

 10. The seventh or last true rib. 11. The costal cartilages of the true ribs. 12. The 

 two last false ribs the floating ribs. 13. The groove along the lower border of the 

 rib for the lodgment of the intercostal vessels and nerve. 



