340 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
most two or 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 fromthe spinous processes of the last two or three: 
vertebre, 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') 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 hemal arch below the noto- 
chordal filament ; passing upwards and backwards it crosses the 
dorsal portion 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’), the base resting on the 
fin rays. It arises from the ‘ flossentriiger ’ and the bodies and hemal 
processes of the last two or three vertebre, the very lowest portions 
arising from the extremities of the hwmal processes of the fourth and 
fifth vertebre (counting from behind) not reaching up to the centra. 
Numerous tendons run along the muscle, as a rule ofe 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 .7.e., dorsal 
or ventral, as the case may be,) to it. Certain of the fibres of each 
