CHAPTEE IV. 



MODIFICATIONS OF THE SKELETON. 



The lowermost sub-class of fishes, which comprises one 

 form only, the Lancelet {Branchiostoma [s. AmpMoxus] lanceo- 

 latum, possesses the skeleton of the most primitive type. 



Fig. 28. — Branchiostoma lauceolatum. 

 a, Mouth ; b, Vent ; c, abdominal porus. 



The vertebral column is represented by a simple cJiorda 



-^^^ 



Fig. 29. — Anterior end of body of Branchiostoma (niagn.) 



d, Chorda dorsalis ; e, Spinal chord ; /, Cartilaginous rods ; g, Eye ; 



h, Branchial rods ; i, Labial cartilage ; k, Oral cirrhi. 



dorsalis or oiotochord only, which extends from one extremity 

 of the fish to the other, and, so far from being expanded into 



