NILS ROSEN, STUDIES ON THE PLECTOGNATHS. 9 



except the most caudal part, separating the dorsal body- 

 rauscles of each side from each other. The enlargement of 

 these fin-muscles 'is of great interest, as I consider that it shows 

 the manner in which the museles of Mola have developed. 

 The Ostraciontids, or trunk-fishes, have, as is weJl known, 

 the body encased in an immovable carapace. Only the tail 

 is free and movable. The body-muscles hade been influenced 

 by this arrangement. They form, as has been shown, three 

 distinct museles on each side, which are attached to the 

 caudal peduncle. They move the tail. The caudal museles 

 are present. The pterygiophores of the dorsal and anal fins 

 are firmly connected with the neural, resp. haemal spines, 

 and the profound museles of these fins are very enlarged. 

 They act mainly as inclinators of the fins. In the next 

 section of this series of studies I intend to deal with the 

 skeleton. I shall then give a detailed account of the struc- 

 ture of the articulation between these fins and their ptery- 

 giophores. 



Molidae. 



Several authors have dealt with the »body»-muscles of 

 Mola, as Meckel, Goodsir, Turner, Cleland, Wahlgren 

 and others, but the descriptions are insufficient and in some 

 parts incorrect. I have examined two fullgrown specimens 

 of Mola (Fig. 10—14). 



When the thick and härd skin is removed a large mäss 

 of museles is observed, divided into two parts by a strong late- 

 ral septum of härd connective tissue. The dorsal portion of 

 the musele takes its origin from the cranium, the skin and the 

 vertebral column, with which the pterygiophores are firmly 

 united. The musele mäss consists of several portions which 

 are more or less distinct. Each portion continues into a 

 tendon. All the anterior tendons, 19 in number, are inserted 

 into the rays of the dorsal fin. The first and second tendons 

 are united to the first ray, the third and fourth to the 

 second one. To each of the other rays only one tendon is 

 attached. Each portion shows an exteriör large part and an 

 interiör smaller one. The interiör part has a reddish- 

 grey colour, the exteriör is white. The interiör origina- 

 tes only from the vertebral column and the bones formed 



