ICHTHYOPSIDA. 229 
two distinct regions, an abdominal and a caudal. The abdo- 
minal vertebrae possess a superior or zeural arch, for the pas- 
sage of the spinal cord, a superior spinous process, and two 
transverse processes to which the ribs are attached. The caudal 
vertebrze have no marked transverse processes ; but, in addition 
to the other parts already mentioned, they give off an inferior 
or hemal arch, below the body of the vertebra, and they carry 
inferior spinous processes (fig. 123, 4). The rvzbs are attached 
to the transverse processes or to the bodies of the abdominal 
vertebree (fig. 123, 7) ; and they do not enclose any thoracic cavity, 
or protect the organs which are usually contained in the chest 
—namely, the heart and breathing-organs. The anterior or 
lower ends of the ribs of fishes are free, or are rarely united to 
iy 
J 
—\ ea Rares 
= yyy > 
ESS 
= iN 
Fig. 123.—Skeleton of the common Perch (Perca fluviatilis). p Pectoral fin ; 
vy One of the ventral fins; @ Anal fin, supported upon interspinous bones (2) ; 
¢ Caudal fin; d First dorsal fin; a’ Second dorsal fin, both supported upon inter- 
spinous bones; zz Interspinous bones ; ~ Ribs ; s Spinous processes of vertebre ; 
A Heemal processes of vertebre. 
hard productions of the integument; but there is never any 
breastbone or szermum properly so called. 
The only remaining bones of the trunk proper are the so- 
called “interspinous bones” (fig. 123, 2 2). These area series 
of pointed dagger-like bones, embedded in the middle line of 
the body, between the great lateral muscles which form the 
greater part of the body of a fish. The inner ends or points of 
the interspinous bones are attached by ligament to the spinous 
processes of the vertebrae, and at their outer ends they support 
