. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 178 BttUefin Mus-eiiw of Comparative Zoology, Vol. 135, No. 3 Fig. 8. Chimaera colliei. Muscles of the left pectoral region, lateral view, , Adductor superficialis; , dorsal constrictor muscle; , latero-ventral muscle; , protractor dorsalis pectoralis; , retractor dorsalis pectorolis; , retractor latero-ventralis pectorolis externus; , retractor pectoralis superior; scop., scapula; , trape- zius externus muscle. insertion, and fiber direct
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 178 BttUefin Mus-eiiw of Comparative Zoology, Vol. 135, No. 3 Fig. 8. Chimaera colliei. Muscles of the left pectoral region, lateral view, , Adductor superficialis; , dorsal constrictor muscle; , latero-ventral muscle; , protractor dorsalis pectoralis; , retractor dorsalis pectorolis; , retractor latero-ventralis pectorolis externus; , retractor pectoralis superior; scop., scapula; , trape- zius externus muscle. insertion, and fiber direction of each differ slightly, clearly a more specialized arrange- ment. Since the scapular process of holo- cephalians rises above the level of the horizontal septum, there are also epaxial fibers which insert upon it. In sharks the epaxial muscles are not involved in the shoulder musculature. In contrast to the more highly differen- tiated state of the holocephalian shoulder groups, the muscles which are associated with the coracoid region may be simpler than those of sharks. The bases of the coracobranchials are not fused into common coracoarcuals as they are in elasmobranchs. The coracohyoid muscles actually originate on the coracoid cartilage rather than on the fascia over the muscles anterior to it. These aspects of the hypobranchial musculature outweigh, in Shanns mind, the seemingly special, massive development of the cora- comandibularis, and he emphasizes his im- pression that the Holocephali are in these structural arrangements more primitive than the sharks and rays. From the musculature of the paired fins few inferences may be drawn concerning the relationships of the Holocephali. Again, in principle, the fin muscles of all fishes are much alike. To raise, depress, and twist the fins all that has proved necessary are a dorsal and a ventral muscle mass, some fibers of which are drawn into the fin over an oblique course. The holocephalians present l)ut one modification
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