THE CARAPACE, 1 3 



plates, thus forms a continuous osseo-cartila- 

 ginous rod. 



12. Examine the Ribs.— Attached opposite the inter- 

 spaces between the vertebral bodies from the first to the 

 fourth dorsal, and articulating either only with the inter- 

 posed cartilage, or also with the posterior end of one 

 centrum and the anterior end of the next, are the 

 heads {capitidd) of the second, third, and fourth ribs. 

 a. From the capitula, thin bony bars, which may 

 conveniently be called the necks of the ribs, run 

 outward and dorsally for a short distance, and 

 then fuse with the ventral aspect of the costal 

 J>/afes already mentioned (lo, ^). 

 ^. The costal plates by their inner ends articulate 

 with the neural plates of the two vertebrae be- 

 tween which the head of the corresponding 

 rib lies. 



y 



13. The arrangement of the fifth, sixth, seventh, and 

 eighth ribs is like that described above (12), except 

 that each articulates with the centrum of only one dor- 

 sal vertebra (that which corresponds 'in number with 

 the rib) ; and the costal plate of the ninth rib articu- 

 lates only with the neural plate of its own vertebra. 

 In old specimens, also, the sides of the centra of the 

 posterior dorsal vertebrae bear distinct capitular pro- 

 cesses, to the ends of which the heads of the ribs are 

 attached. 



14. The ribs of the first pair are very small ; they 

 run backward and outward from the sides of the cen- 

 trum of the first dorsal vertebra, and fuse at their outer 



