24 



THE ELASMOBRANCH FISHES 



The scales present in the integument of a shark like Heptanchiis provide a 

 relatively compact exoskeleton which, in a general way, serves to protect the 

 organism against external injury. In form the scales vary considerably de- 

 pending upon their position. The first of these, 

 represented by figure 27a, were taken from the 

 side of the body just above the lateral line. They 

 are therefore from a region which is not unduly 

 exposed and which may be characterized as 

 typical. By looking from the lower left- to the 

 upper right-hand corner it will be observed 

 that the scales are arranged more or less in 

 oblique rows. The same is true, although less 

 evident, if they be observed from the lower 

 right- to the upper left-hand corner of the 

 figure. If a larger piece of the integument be 

 drawn and lines be ruled through the rows of 

 scales, the lines will form a series of rhomboids, 

 producing the diamond-shaped pattern. In such 

 a pattern each scale normally points backward 

 and is attached anteriorly and centrally. 



The details of a single scale have been figured 

 by Steinhard (1903) for Heptanchus cinereus 

 (fig. 28). Here an anterior arm {a.a.) is well 

 im1)edded in the integument and a posterior 

 spine {sp}) projects more or less sharply up- 

 ward and backward. Two lateral arms appear 

 (La.) which, as a rule, curve more or less up- 

 ward and terminate in lateral spines (sp.-). 

 Passing along the middorsal line from the an- 

 terior arm to the tip of the posterior spine is the 

 primary or axial crest (cr.^). Located on the 

 lateral arms and branching from the primary 

 crests are the lateral crests (cr.-). Other terti- 

 ary crests (cr.^) connect primary and secondary 

 crests, and a fourth {cr^) arises from the sec- 

 ondary crests to pass laterally around the sides 

 of the scale. Lying deeply buried in the integu- 

 ment is the enlarged supporting base (ba.) 

 which, in general, is rhomboidal in shape and is 

 attached by a narrow neck or pedicel to the 

 main body of the scale. Into the lower substance 

 of the base enter strong fibers of connective 

 tissue which anchor the scale to the integument. 

 Where the base may he broad, as in the scales over any of the exposed areas, 

 many such supporting fibers may be present. 



Fig. 27. Scale patterns, Hep- 

 tanchus macidatus. A. From 

 side of body. B. Modified 

 scales from margin of fin. 

 C. Stomodeal denticles from 

 roof of mouth. 



