-340 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



most two oi' three rays above and below, and thus act as divaricators 

 of the rays. 



A deep layer of muscle may be seen on cutting through the attach- 

 ment of the fascia and reflecting the superficial muscles. It consists 

 of two portions separated by the vertebral column. Owing to the 

 direction taken by the terminal filament of the notochord, the two 

 portions are unsymmetrical, that below the column being greater 

 than that above. The dorsal ■portion (Fig. 9, d) consists of a single 

 muscle arising from the spinous processes of the last two or three 

 vertebrae, and passes almost directly backwards. Three or four 

 tendons begin near the origin of the muscle, and are inserted into 

 the bases of the upper three or four rays. 



The ventral 'portion is divisible into two parts. The upper ( Fig. 

 9, v 1 ) is a triangular muscle, imperfectly separable into two parts 

 lying dorsal to the middle line. It arises by an expanded origin 

 from the broad surface of the fourth haemal arch below the noto- 

 chordal filament ; passing upwards and backwards it crosses the 

 dorsal poition before its insertion, and dividing into two long tendons 

 is inserted into the axial surfaces of the two upper fin rays. It 

 pulls them downwards towards the middle line as well as laterally, 

 and thus acts as an opponent of the uppermost tendons of the super- 

 ficial layer, and aids the intrinsic muscles. The lower part forms a 

 broadly triangular muscular mass (Fig. 9, v 2 ), the base resting on the 

 fin rays. It arises from the ' flossentrager ' and the bodies and haemal 

 pi^ocesses of the last two or three vertebra?, the very lowest portions 

 arising from the extremities of the haemal processes of the fourth and 

 fifth vertebrae (counting from behind) not reaching up to the centra. 

 Numerous tendons run along the muscle, as a rule one for each ray, 

 into the bases of which they are inserted. The lowermost portiors 

 are inserted into the rays imbedded in the adipose tissue, which are 

 not functionally parts of the fin. This part of the muscle aids the 

 superficial musculature, the lower fibres serving to approximate the 

 rays. 



The intrinsic muscles (Fig. 8, It), lie immediately below the integu- 

 ment posteriorly to the attachment of the fascia. One muscle is sup- 

 plied to each ray of the fin proper, none being inserted into the fins 

 in the adipose tissue. Each arises from the abaxial surface of a ray, 

 and is inserted into the axial surface of the next external K i.e., dorsal 

 or ventral, as the case may be,) to it. Certain of the fibres of each 



