A SEGMENT OF THE SKELETON. 19 



cessor or successor in the series. The transverse ijrocesses are 

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

 (T.t) articuhites with the tuherculuin of the rib, the Litter 

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

 intular and tuhtrcular transverse processes respectively. Each 



Fig. 5. — A sej»Tnent of the endoskeleton in tbo anterior thoracic rej^ion of the body of a croc- 

 odile. — (7, the centrum or body of the vertebra ; N.S., tlio neural spine ; Z, the prezy- 

 gapophysis ; Z', the postzygapophyais ; T.t, the transverse process which articulates 

 with the tuberculum of the rib {t) ; Cp.t, that which articulates with the capitulum of 

 the rib \Cp); F.r, tlie ossiQed vertebral rib; V.r', the part of the vertebral rib which 

 remams cartilaginous ; St.r, the sternal rib ; St^ 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 ( Fir') ; 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 ( Cp), 

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

 sified but unsegmented cartilage, which forms the sternum {8t), 

 A cartilaginous, or partly ossified, i«nciW<ife/)rocess (P.w.) 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 Vertebrafa, the caudal vertebrne 

 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- vertebrjc, 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- 



