LATERAL MUSCLE IN TELEOSTEI. 333 
that this triangle represents the base of a pyramid which con- 
verges to an apex on the centrum*. ‘Tracing the sixth myomere 
backwards through the width of a myomere, we should find it to 
show the appearance of No. 5 in the text-figure ; it has then been 
thrust from contact with the vertebral column by the appearance 
of a new pyramid: moreover, it has made its anterior superficial 
appearance dorsally. Backwards again through the width of 
another myomere it has the appearance of No. 4; here a consider- 
able portion of it is visible externally, both dorsally and just 
above the “‘red fibres”; in this and in its next stage, No. 3, it 
‘appears in section as two quadrangular faces which are approaching 
one another. In No. 2 we are able to see how the two faces, 
whose superficial continuations are now recognisable as the mesio- 
dorsal (J7.D.) and latero-dorsal (Z.D.) portions respectively, 
become confluent. Passing from this point through the width 
of another myomere the two faces are found fused into one 
triangular area (1, in section), which is invisible externally owing 
to the convergence of the faces of the myomere next in front. 
By dissection it can be demonstrated that this triangle forms 
the base of a pyramid whose apex is attached to the vertical 
septum. 
Thus it is seen that the dorsal moiety of a myomere is com- 
posed of two opposed hollow pyramids, a dorsal one directed 
inwards and backwards, and a ventral one directed inwards and 
forwards. They are not divided by a septum but share a common 
face, which may be seen in the text-figure at the areas marked 
2, 3, 4, and, in part, 5 in the Z.D. portion of the section f+. 
The ventral moiety of the myomere takes a course symmetrical 
with the dorsal, which it resembles in all essential points of 
structure. 
Before leaving this figure it would be well to observe that it 
serves admirably to indicate why there is but one change in 
direction of the external fibres, correlated with the change which 
the conical structure involves, in each moiety of the myomere, 
instead of the two which one would be led to expect. Following 
the central course of myomere No. 4, it is seen that only the 
fibres above the mesial plane of the Z.D. portion, and below that 
of the Z.V. portion, are visible at the surface. The fibres below 
the mesial plane of the Z.D. portion and above that of the Z.V. 
portion, which take the opposite directions respectively to those 
named in the preceding sentence, are only found in myomeres 5 
and 6; and these do not appear on the surface. 
I have also followed the course of the myomeres in the dorsal 
moiety of a young Salmon through over a hundred consecutive 
sections from the pelvic region. Two such sections are repro- 
duced here (text-fig. 3) to indicate the directions of growth and 
diminution in seven consecutive myomeres. As corroborative 
* This will be corroborated in the remarks on sections of a young Salmon, p. 334. 
+ It is evident that this area may be regarded as the forward continuation of a 
pyramid similar to 1, or as the backward continuation of a pyramid similar to 6. 
