110 SKELETON. 



of resemblance among the ribs, yet there are, also, some well 

 marked peculiarities. The ribs increase successively in length 

 from the first to the seventh inclusively ; they then decrease : 

 the last is not only the smallest, but not unfrequently the shortest. 

 The angles of the ribs increase in their distance from the spine, 

 from the first to the last rib. The angle, however, of the first 

 rib, is not well marked, from its being so near the tubercle; 

 neither is the angle of the last, from its being so near the ante- 

 rior extremity. The oblique ridges constituting or marking 

 off the angles, are placed one above the other, in the same line. 

 This gives to the back of the thorax a triangular flatness, the 

 base of which is below. The projection backwards of the angles 

 of the ribs, along with that of the spinous processes of the ver- 

 tebrae, forms on each side of the latter the gutter, which is filled 

 up by the large muscles that keep the trunk erect. This gutter 

 is, of course, broader below. 



The first rib is more circular than the others. Its head is 

 spherical, instead of presenting two articular surfaces. This 

 rib is flat above and below ; its margins are internal and exter- 

 nal. It has no groove for the intercostal vessels and nerve. 

 About the middle, the upper surface is marked by a superficial 

 oblique fossa, made by the subclavian artery ; in front of, and 

 behind which is a small rising, marking the insertion of the sea- 

 leni muscles. The second rib is considerably longer than the 

 first, and has its flat surfaces obliquely upwards and down- 

 wards, so as to round off that part of the thorax. The four in- 

 ferior ribs decrease at their anterior extremities, or become 

 somewhat tapering. The last two ribs do not articulate with 

 the transverse processes, and, consequently, have no corre- 

 sponding tubercles. As their heads articulate with the middle 

 of the bodies of their respective vertebrae, instead of with the 

 margins, they present only a single and somewhat convex sur- 

 face. The eleventh rib is marked only for a short distance in 

 its middle by the fossa, for the intercostal vessels. The twelfth 

 rib has no mark of the kind. 



There is an augmentation in volume from the second to the 

 eighth rib, inclusively; afterwards they decrease. The angles 

 of the ribs are, successively, more and more obtuse. 



The structure of the rib is spongy, covered with a lamella of 



