444 ME. ST. GEOEGE MIVAET ON THE 



The Tenth Bib. 



This rib (normally anchylosed in the adult with the sacrum and pelvis) generally 

 appears as an elongated ventrally produced process (figs. 70, 71, 72, & 73, pi) of the 

 twenty-seventh vertebra, as therein noticed. The rib is compressed from within 

 outwards (fig. 1, x). 



The tenth is only about from f to f as long as the ninth rib, and may be somewhat 

 shorter than the second rib when this latter is measured from the root of the tuberculum 

 distad. Its inner (here actually postaxial) surface between the tuberculum and capitulum 

 is but very sUghtly concave ; its preaxial margin is convex, and its postaxial one concave. 



On the postaxial side of the expanded proximal part of the rib is a large pneumatic 

 opening. 



The ridge, which in more preaxial ribs ascended the outer surface of the shaft to the 

 interval of the head and tubercle and went on ultimately to the tubercle, is here pro- 

 duced into a sharp crest, which is the actual outer and preaxial margin of the shaft of 

 the rib, and which lies close to that margin all the way to the dorsal extremity of the 

 tuberculum. 



An Eleventh Bib 



may be developed, which then closely corresponds with the conditions here attributed 

 to the tenth rib. When this development occurs, the tenth rib approximates in its form 

 very nearly to what has here been described as the ninth rib. 



The Sternal Eibs. 



These six ribs increase gradually in length postaxially from the first to the sixth ; so 

 that the fourth is rather more than twice the length of the second, and the sixth is from 

 two and a half to three times the length of the second ; the third is more than half the 

 length of the sixth (fig. 1, ii, in, iv, v, vi). 



The sternal ribs are greatly expanded dorso-ventrally at their distal (sternal) ends, but 

 do not bifurcate and divide into two processes like the tuberculum and the capitulum 

 of the vertebral ribs. 



All these ribs, except the first, unite with one or other of the vertebral ribs by a 

 distinct joint. 



The angle formed by the second sternal rib with its vertebral rib is only slightly 

 obtuse, viz. about 129°; the angle formed by the third sternal rib with its vertebral rib 

 is more obtuse, viz. about 140°. 



The fourth sternal rib continues on the curve of its vertebral rib, while the fifth 

 sternal rib cannot be said to form any angle other than 180° with its vertebral rib. 



The First Sternal Bib. 

 This rib (fig. 76, i & i'), of which I have not been able to see an adult specimen, 

 seems (from the immature skeleton) to be a subcylindrical bone but little expanded at 



