The Anatomy of Chlamydoselachus 381 



intercalaria, as if the radials had originated, like those of the dorsal and anal [fins] in- 

 dependently, and afterwards through downward growth had in the greater portion of the 

 extent come in contact with the neural processes. These radials and interneurals are 

 not fused like the radials and haemapophyses" (Garman, 1885.2, p. 16). With this 

 interpretation Goodey (1910.1, p. 553) seems to agree, for he says: "The dorsal radial 

 supports of the caudal fin I do not consider as dorso-spinalia, because at their commence- 

 ment anteriorly they are not always continous with the neural arches, and, moreover, 

 there is as much evidence to show that in general they originate independently of the 

 vertebral column as there is in favor of their being portions segmented off from the dorsalia 

 below them." 



In the section on external characters, attention has been called to the shortness of 

 the cartilaginous fin rays of Chlamydoselachus, as compared with their condition in one 

 of the most primitive of fossil sharks, Cladoselache. We are now in a position to ask, 

 is there any evidence, in the patterns of the fin skeletons, to support the view that the 

 somewhat rudimentary character of the appendicular skeleton in Chlamydoselachus is 

 secondary, not primary? Along with the fusion of radials to form basals, radials are 

 found breaking up into segments which do not always retain their original alignment. 

 The shapes of these segments are sometimes irregular. As indicated by Woodward 

 (1921), this fragmentation and displacement of typical parts seems to indicate retro- 

 gression. The shortness of the radials is presumably due to arrested development. 



THE MUSCULAR SYSTEM 



Only the skeletal or voluntary striated muscles are considered here. Little is known 

 concerning smooth muscle and cardiac muscle_ in Chlamydoselachus, and in any case 

 these are best considered in connection with the organs of which they form a part. It is 

 convenient to classify the skeletal muscles upon an embryological basis. In Chlamy- 

 doselachus, as in other vertebrates, most of these muscles may be assigned to two great 

 groups, the metameric muscles and the branchiomeric muscles. The great muscles of the 

 body wall are metameric muscles. The branchiomeric muscles are of visceral-arch origin, 

 but they do not include all the muscles attached to the visceral skeleton. 



THE METAMERIC MUSCLES 



The metameric muscles of fishes are divisible into two groups : the axial muscles, in 

 which the metamerism is clearly expressed even in the adult; and the appendicular muscles 

 or fin muscles. In the latter, the metameric condition is seldom recognizable in the adult; 

 nevertheless, in primitive fishes the appendicular muscles arise from the metamerically 

 arranged myotomes of the early embryo. 



