22 ON THE APPENDICES GENITALES (CLASPERS) IN THE SELACHIANS. 



attached to this piece, but always found it placed at another level than that of the nearest rays, and 

 1 take it to he a specially separated part of the stem-skeleton. 



The muscular system (see pi. V and VI | does not show the rich variation found in the 

 skeleton, being upon the whole rather uniform, which is a natural consequence of the fact that the 

 part of the skeleton, particularly multifarious both as to the number and form of the single pieces, 

 viz. the terminal part, has no muscles of its own; the muscles (generally) only acting on the terminal 

 part as a whole. 



Only the medial side of the fin-muscles has been specially developed in the male; the muscles 

 spreading over the lateral parts of the fin, i. e. the ray-muscles of the upper and lower side, and the 

 dorsal layer originating from the lateral muscles of the body, are chiefly the same in both sexes, 

 and show in the different forms examined so very few differences that I, also in the special part, pass 

 over them. 



In the medial muscular system may be distinguished between a more proximal and a distal 

 part, not however strongly separated, especially not so in man}' Plagiostomes, while in the Holoce- 

 phales the separation is more distinct, the appendage of the latter being more independent of the fin. 



In the Plagiostomes I generally find the same type, as has been described in the Greenland 

 Shark. The proximal part consists of a Muse, adductor (ef depressor) pinner (ef appendicis) (A), and a 

 M. extensor appendicis (E). Muse, adductor does not in any of the forms examined by me show any 

 separation into an independent, superficial ventral layer, and a deeper, more dorsal one, but forms a 

 whole 1 ); the ventral side, however, appears to a great extent separated into single bundles correspon- 

 ding to the ray-muscles, while the dorsal side shows nothing of the kind. The fibres arise from the 

 pelvis, as well from the ventral, as, though often to a smaller extent, from the dorsal surface, as also 

 from a tendinous stripe prolonging, as it were, the hindmost edge of the pelvis into the median line; 

 they run obliquely-laterally , and are inserted on the basale, on the following joints (£,, b 2 etc.), and on 

 the proximal end of the appendix-stem; often, however, the superficial medial fibres run on and mingle 

 with the M. dilatator. The fibres forming the medial marginal part, run almost straight from before 

 backward, and form always a solid mass not divided into separate bundles; the foremost, lateral parts 

 (as in the Greenland Shark) are coalesced with the deeper-lying ray-muscles. 



M. extensor {appendicis) (£) is mostly a rather flat muscle, situated on the dorsal side of the 

 previous one; it originates on the medial side of the basale, often moreover on the pieces /;„ b 2 , etc., 

 and is inserted on the appendix-stem, usually at the proximal end, but sometimes farther backward, 

 and the hindmost part of this muscle then spreads in a cloak-like manner over part of J\L dilatator 

 (comp. the Greenland Shark). This muscle generally is very distinct, already in quite young animals 

 with undeveloped appendages; but in Lamna I find its fibres woven into those of M. adductor to 



a coalescing of basal parts of rays, refers to the fact that such a coalescing of rays is frequently seen in other parts of the 

 fin, especially anteriorly, he does not see that the basal joints of the rays always are many times longer than the distal, and 

 that this difference of size is also preserved by such concrescences. 



■I The type of the arrangement of the ventral muscular system put down by v. D a vidoff (L c. p. 456) for Heptanclrus 

 9, which reminds of the arrangement in Chimara, I have had 110 occasion to see in any Plagiostome; v. D. asserts to have 

 found it very generally, and refers to Acanthias almost as an exception; however, I can with certainty see no other forms 

 mentioned in his text than Carcharias as belonging to the same tvpe as Heptanclius. 



