CLELAISTD ON TUE ANATOMY OF THE SllOUT SUN-FISH. 177 



ossseous vertebra, against which each abuts, aa well as from the 

 superficial aponeurosis; the former arise, in addition, for some 

 distance along the fibrous septum of the middle lateral line, and 

 overlap the posterior muscles of the dorsal fin. 



The muscles of the dorsal and anal fins demand a more detailed 

 description. The individual muscles of which they are composed 

 are not entirely distinct ; they run into one another to a certain 

 extent ; but they are arranged on a definite plan ; and this plan is 

 the same in both. The typical arrangement is this : each muscle 

 consists of two triangular laminfe, a superficial and a deep, con- 

 nected anteriorly by a tendon directed obliquely backwards, and 

 incloses between its layers the succeeding muscle, Avhile it is itself 

 similarly surrounded by the muscle in front. Its posterior fibres are 

 longest and most vertical, and form the base of the triangle ; the 

 most anterior fibres are short and oblique, forming the apex. 

 (Pt. VI. fig. 3), The superficial lamina arises principally from the 

 fibrous septum of the lateral line ; but, at its posterior part, where 

 it extends beyond the muscle in front, it arises also from the 

 superficial aponeurosis. The deep lamina arises from the interspi- 

 nous bones and intervening processes of vertebrae. 



The tendons after quitting the muscles become more vertical, and 

 lie in very loose watery areolar tissue till they reach the cartilaginous 

 piUows at the extremities of the interspinous ranges. They are then 

 received into deep perpendicular grooves which are completed into 

 tubes by the tough integumentary tissue. Mr. Turner, in his notes, 

 describes an arrangement by which the tendons are lubricated in these 

 tubes : viz. a very loose and watery areolar tissue confined in sittt, by a 

 thin but dense layer of membrane which lines the tube, extends beyond 

 it, and is reflected thence to the surface of the tendon, like the theca of 

 a tendon in the human subject, for example. Of course the most an- 

 terior muscles, especially of the dorsal fin, deviate a good deal from 

 what is here given as the characteristic arrangement, but generally 

 there is the same pennate disposition of fibres, and the same sheath- 

 ing of one muscle within another. 



To the joints and movements of the dorsal and anal fins Mr. 

 Groodsir particularly directs my attention. He points out that, 

 while in fishes generally there is a distinct joint for each interspinous 

 bone and fin ray, and each of the latter moves independently ; in the 

 ■sun-fish the cartilaginous bases of the dorsal and anal fin rays 

 respectively are compacted together to form a single body, trans- 

 versely convex, which moves in one mass in a corresponding 

 concavity of the cartilaginous pillow, the surfaces being lubricated 

 by watery connective tissue, such as has already been referred to. 



Instead of beiag compound organs whose motions are the 

 result of the harmonious movements of the constituent simple 

 organs, the dorsal and anal fins of the sun-fish are each a single 

 organ, moving on a single joint. As regards the method of their 

 movements : — the sun-fish being destitute of a great lateral muscle 



