THE ELASMOBRANCH FISHES 



83 



may be further segmented {Gin(jliimostoma) or they may be absent (Squatina, 

 fig. 89b) ; or, finally, all the basal segments may fuse into a single basal plate 

 (Heptanchus, Heterodontus, fig. 88). In certain forms the basals may come in 

 contact with the column. Such a condition occurs in Squatina (fig. 89b), 

 Rhinobatis, and Pristis, in which numerous segments in front of the fin may 

 be present joining the neural spines. 



Fig. 89. Dorsal fin skeleton of Elasmobranchs. (From Mivart.) A. Mustehis antarcticus. 

 B. Squatina. C. Baja. 



h.c, basal cartilages; h.c.^, median segments; h.c.", distal segments. 



The skeleton of the anal fin, like that of the other unpaired fins, is made up 

 of two or three different types of segments, which, in general, show modifica- 

 tions similar to those in the dorsals. 



