LATERAL MUSCLE IN TELEOSTEI. 329 
evolution of animals, and is merely noted here as a bye-way 
which might repay exploration. 
Summary of the external divisions of the lateral muscle :— 
. Supracarinalis. 
. Dorsal moiety. 
(a) Mesio-dorsal portion. 
(6) Latero-dorsal portion. 
3. “ Red Muscle.” 
(Lateral Line.) 
*“ Red Muscle.” 
. Ventral moiety. 
(a) Latero-ventral portion. 
(6) Mesio-ventral portion. 
6. Infracarinalis. 
Js) | 
Oe 
(2) Internal Structure. 
In the foregoing section we have named the outstanding 
superficial divisions of the lateral muscle in Teleosteans. Let us 
now proceed to prove by dissection to what extent these external 
markings are evidence of internal structure. Enough has already 
been said of the carinales and of the “red muscles ” to show that 
these are specialised offshoots from the lateral muscle ; and, since 
all the authors who have mentioned them are agreed as to their 
morphological value, it would be superfluous to treat of them at 
greater length in the present paper ; suffice it to say that there 
is no question of their division into more than one stratum, 
nor are they themselves regarded in the light of strata, deep or 
superficial, of the lateral muscle. Let us concentrate our attention 
upon the dorsal and ventral moieties of the main mass of the 
lateral muscle. 
With the exception of Owen and McMurrich, all the authors 
whom I have quoted maintain the completeness of the division at 
the lateral line. Dissection shows a well-marked septum running 
continuously from beneath the lateral nerve to the bodies of the 
vertebre. The lateral line, then, must be regarded as the 
external evidence of a true horizontal division of the lateral 
muscle. 
Having established this fundamental division, let us enquire 
to what extent the dorsal moiety may legitimately be subdivided, 
It has been shown that it comprises superficially, («) a mesio- 
dorsal portion, in which the fibres of each myomere are directed 
from above anteriorly to below posteriorly, and (6) a latero-dorsal 
portion in which the fibres take the opposite direction. On 
stripping the superficial fibres from the latero-dorsal portion of a 
typical myomere such as occurs in the caudal region, it is found 
that the direction of the underlying fibres gradually changes so 
as to become, first, parallel with the long axis of the body, and 
then, very near to the vertebral column, from above anteriorly 
