RIBS TRUE AND FALSE. 



101 



as being situated upon and somewhat behind each extremity of the inci- 

 sura semilunaris of the upper border of the manubrium. These pre 

 sternal or supra-sternal pieces, \vhich are by no means constant, appear at 

 about the thirty-fifth year. Beclard considers them to be the analogue 

 of the fourchette of birds, and Breschet as the sternal ends of the cer- 

 vical rib. 



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

 angularis sterni, aponeurosis of the obliquus externus, internus, and trans- 

 versal is muscles, rectus, and diaphragm. 



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

 connected with the sternum, and hence named sternal or true ribs ; the 

 remaining five are the asternal or false 

 ribs ; and the last two shorter than the 

 rest, and free at their extremities, 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, and 

 with the exception of the last two 

 are broader at the anterior than at the 

 posterior end. The first rib is hori- 

 zontal in its direction ; all the rest are 

 oblique, so that the anterior extremity 

 falls considerably below the posterior. 

 Each rib presents an external and in- 

 ternal surface, a superior and inferior 

 border, and two extremities ; it is 

 curved to correspond with the arch 

 of the thorax, and twisted upon itself, 

 so that, when laid on its side, one 

 end is tilted up, while the other rests upon the surface. 



The external surface is convex, and marked by the attachment 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, f Near its vertebral 

 extremity, the rib is suddenly bent upon itself; and opposite the bend, 

 upon the external surface, is a rough oblique ridge, which gives attach- 

 ment to a tendon of the sacro-lumbalis muscle, and is called the angle. 

 The distance between the vertebral extremity and the angle increases 

 gradually, from the second to the eleventh rib. Beyond the angle is a 



* 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 tubercle. 10. The seventh or 

 last true rib. 11. The costal cartilages of the true ribs. 12. The last two false ribs or 

 floating ribs. 13. The groove along the lower border of the rib. 



f This groove is commonly described as supporting the intercostal artery, vein, and 

 nerve, but this is not the case. 



