BONES OF THE TRUNK. 



2] 



apex presents a cordiform 

 opening, and the opening 

 at the base has a large 

 notch in front. 



Fig. 7. 



STERNUM. 



Is an oblong, slightly- 

 curved bone, placed in front 

 of the thorax. Usually it 

 consists of three pieces, 

 but in advanced life of but 

 one. 



The first or superior 

 bone,* is the thickest, and 

 resembles in shape a trian- 

 gle with the corners cut 

 oft", the base being upwards ; 

 on the superior edge is a 

 concavity for the benefit of 

 the movements of the tra- 

 chea ; on each side is a 

 large concavity for the ar- 

 ticulation of the clavicle, and below are two smaller ones for the 

 articulation of the first, and part of the second rib. 



The second bone^ is longer and narrower than the first, increasing 

 in breadth in its lower extremity ; its sides present pits for the 

 articulation of part of the second, the third, fourth, fifth, sixth, and 

 part of the seventh ribs. 



The tliird bone,^ is very frequently cartilaginous, and called 

 xyphoid or ensiform ; its shape varies ; sometimes being pointed, 

 and sometimes bifurcated ; upon its side is a depression for a portion 

 of the seventh rib. 



RIBS. 



These are twenty-four in number, twelve on cither side; those 

 that articulate with the sternum are called true ribs, and are seven 

 in number ; the five below them are called false ribs : in some rare 

 instances there have been thirteen or eleven ribs on one side. They 

 are parallel, and directed obliquely downwards and forwards ; each 

 having a parabolic curve, and gradually increasing in size until the 

 eighth, afterwards gradually diminishing. 



The anterior or sternal extremity is larger and flatter than the 

 j)Ostei"lor ; the posterior or vertebral extremity presents a spherical 

 head, having two articular surfaces separated by a ridge ; surrounding 

 the head, the rib is very narrow and called the neck, the upper edge 

 of which is sharp for the insertion of the internal transverse liga- 



