THE BONES OF THE TRUNK 



45 



anterior extremity presents the usual oval pit for the first costal 

 cartilage, its direction being horizontal from before backwards 

 The first rib has no subcostal groove. 



The Second Rib. — The surfaces of the shaft of this rib occupy a 

 transitional plane between that of the first and those of the suc- 

 ceeding ribs. It is practically destitute of a twist. The neck is 

 compressed from above downwar .' s, 

 and from before backwards. The 

 distinctive character of the bone is 

 the presence on its supero-extemal 

 surface, near the centre, of a rough 

 oval eminence for a portion of the 

 first and the second slips of the 

 serratus magniis. Behind this im- 

 pression the surface gives insertion 

 to the scalenus posticus. 



The Tenth Rib. — This bone may 

 or may not be peculiar. If the 

 body of the ninth thoracic vertebra 

 has a lower demi-facet, there is 

 nothing peculiar about the head of 

 the tenth rib. If, however, the 

 lower demi-facet is wanting on 

 the ninth thoracic body, the head 

 of the tenth rib has only one facet 

 for that on the body and pedicle 

 of the tenth thoracic vertebra. The 

 tubercle has usually an articular 

 facet for the tenth thoracic trans- 

 verse process, but this may be 

 awanting. The angle and subcostal 

 groove are well marked. 



The EUeventh Rib.— The head of 

 this rib has one facet for that on 

 the pedicle of the eleventh thoracic 

 vertebra. There is a sUght tubercle, 

 destitute of an articular facet, a 

 faint angle, and an equally faint 

 subcostal groove. The anterior ex- 

 tremity is pointed, and only tipped 

 with a costal cartilage, which is free. 



The Twelfth Rib.— This is a very short bone. Its head has one 

 facet for that on the pedicle of the twelfth thoracic vertebra. The 

 tubercle, angle, and subcostal groove are awanting. The shaft is 

 very narrow, and terminates anteriorly in a pointed extremity, 

 which is merely tipped with a free costal cartilage. The lower 

 border of the shaft has a rough, sharp outUne, and gives attachment 

 to a portion of the quadratus lumborum muscle, whilst the upper 

 border, especially towards the back part, is smooth and round. 



Fig. 31. — The Eleventh 

 Twelfth Ribs of the 

 Side (Inferior View). 



AND 



Left 



