THE CARAPACE. 13 



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 (capituld) 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 

 plates already mentioned (lo, i). 



b. 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. 



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 vertebras 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 



