624 
SCANDINAVIAN FISHES. 
part of each ray in the dorsal tin. The flexors of the 
anal tin, also divided into a surface-layer and an under- 
layer, originate from the bodies of the hindmost ab- 
dominal vertebrae, from the caudal vertebrae with their 
inferior processes and interhaemal bones, and from the 
under surface of the horizontal fibrous membrane, and 
are attached to the rays of the anal tin in the same 
manner as we have just described in the case of the 
flexors of the dorsal tin. The flexors of the caudal tin 
sf mpd 
mpa , \ 
Fig. 156. Position of the muscles and viscera in Orthagoriscus mold, 
on a reduced scale. After Cleland. 
mpa , the flexors of the anal fin ( musculi pinnce analis ); s/, the 
fibrous dividing membrane ( septum fibrosum ) ; mpd, the flexors of the 
dorsal fin ( musculi pinnce dorsalis ) ; maa, the anterior abdominal muscle 
(m. abdominalis anterior ); h , the liver; l , the ligament between the 
intestinal sac and the liver; i, the peritoneal investment of the in- 
testines (intestinal sac); p, the peritoneum, opened and partly removed; 
map, the posterior abdominal muscle (in. abd. posterior)-, a, the vent; 
mpc, the flexors of the caudal fin (m. pinnce caudalis). 
(mpc) form no compact muscular mass; each of the rays 
in the caudal tin is furnished on each side with a spe- 
cial, ventricose muscle, and these muscles start partly 
from the bodies of the hindmost vertebra:', partly from 
the supporting bones of the caudal tin (the hindmost 
interneural and interhtemal bones), partly from the 
superior and inferior folds of the horizontal, inter- 
muscular, fibrous membrane (sf). Of the system of the 
large lateral muscles there remain only two abdominal 
muscles, belonging to the under-layer of the system, 
the first (map) starting from the top of the clavicle, the 
second (maa) from the coracoid bone, and both attached 
to the outer surface of the strong peritoneum (p). So 
great is the modification both of the skeleton and of 
the musculature that has accompanied the late develop- 
ment of the caudal fin, and rendered the dorsal and anal 
fins the principal organs of locomotion. These two fins 
have attached to themselves, from the very beginning, 
the great mass of muscles and supporting bones; while 
the caudal fin has become a secondary organ, which has 
been forced to adapt its development to pre-existent 
circumstances, and which has thus sunk almost to an 
adipose fin, though thin osseous rods have been deve- 
loped to rays within it. The influences of this revolu- 
tion in the development of the organs of motion have 
also affected the central nervous system. The family 
is remarkable, from an anatomical point of view, not 
only for the insignificant size of the brain", which is 
extraordinarily small, even within the class of fishes, 
but also for the fact that the spinal marrow, soon after 
its passage through the occipital foramen, ramifies in 
the well-known “horsetail form” (cauda equina), without 
being continued any further in the form of a continuous 
chord within the spinal canal * * 6 . 
Whether more than two species may be distinguished 
with certainty within this family, must still be regarded 
as a doubtful question. Ranzani’s attempt 0 to establish 
16 species, distributed among 6 genera, has long ago 
been abandoned as futile; and Putnam’s evidence in 
favour of the opinion that the young specimens described 
by Kolreuter, Pallas, and others belong to a distinct 
species of a separate genus seems to require further 
confirmation. It has also been proposed 0 to refer the 
two established species to two distinct genera, one of 
which, Ranzania, with more elongated body and with 
the dermal covering smooth but divided into hexagonal 
plates, has been met with on the English coast, but 
never, up to the present time, within the limits of the 
I Scandinavian fauna. 
“ In large specimens of Orthagoriscus mola, according to Haktjng, the brain may weigh no more than '/ 718 ,, 0 , e - n °t quite 0‘000014, 
of the total weight of the body. 
6 Arsaky, De piscium cerebro et medulla spinali, Halle 1813, p. 4, tab. Ill, fig. 10. 
c Nov. Comm. Acad. Scient. Inst. Bonon. Ill (1839). 
d Proc. Amer. Assoc. Adv. Sc., 19th Meeting (1870), p. 255. 
e Steenstrup and LOtken. Overs. Vid. Selsk. Forh. Kbhvn 1863, p. 42. 
