A SEGMENT OF THE SKELETON. 



19 



cessor or successor in the series. The transverse processes are 

 two on each side, one superior and one inferior. The former 

 {l\t) articulates with the tuberculum of the rib, the latter 

 ( Gp.t) with its capitulum. They may, therefore, be called cw- 

 pitular and tubercular transverse processes resjDectively. Each 



S^i- 



St.r 



Fig. 5. — A segment of the endoskeleton in tlie antenor thoracic region of the body of a croc- 

 odile. — C, the centrum or body of the vertebra; K,8.^ the neural spine: Z^ the prezy- 

 gapophysis; ^, the postzygapophysia; T.t^ the transverse process which articulates 

 ■with the tuberculum of the rib (0 ; QJ.^ that which articulates with the capitulum of 

 the rib {Qpy^ V.r^ the ossified vertebral rib; V.r', the part of the vertebral rib which 

 remains cai-tilaginous ; AY.r, the sternal rib ; *S^ an artificially-separated segment of the 

 sternum ; P.u, the uncinate process. 



rib is divided by an articulation into a vertebral ( V.r) and a 

 sternal {St.r) part. The former remains unossified for a con- 

 siderable distance at its distal end ( Vir') ; the latter is more or 

 less converted into cartilage bone. The proximal end of the ver- 

 tebral rib bifurcates into a tuberculum, {t) and a capitulum ( Qj). 

 The distal end of the sternal rib unites with the more or less os- 

 sified but unsegmented cartilage, which forms the sternum (St). 

 A cartilaginous, or partly ossi^ed, uncinate process (I^.u.) pro- 

 jects from the posterior edge of the vertebral rib, over the in- 

 tercostal space. The student will find it convenient to famil- 

 iarize himself with the conception of such a spinal segment as 

 this, as a type, and to consider the modifications hereafter 

 described with reference to it. . 



In the majority of the. Vertebrata, the caudal vertebra 

 gradually diminish in size toward the extremity of the body, 

 and become reduced, by the non-development of osseous pro- 

 cesses or arches, to mere centra. But, in many fishes, which 

 possess well-ossified trunk-vertebrae, no distinct centra are 

 developed at the extremity of the caudal region, and the 

 notochord, invested in a more or less thickened, fibrous, or 

 cartilaginous sheath, persists. Notwithstanding this embry- 



