336 MR. E. W. SHANN ON THE 
rather pyramids, whose apices are directed backwards, and, below 
them, a series of complete pyramids whose apices are directed 
forwards. 
The incomplete pyramids correspond externally with Humphry’s 
mesio-dorsal portion, and the complete pyramids with his latero- 
dorsal portion. For descriptive purposes this division of the 
dorsal moiety (which is equally applicable to the ventral moiety) 
has its uses. At the same time one cannot insist too strongly 
on the fact that its morphological basis is only slightly more 
secure than that on which Humphry and Maurer framed their 
two-layer hypothesis ; both views depend upon the direction of 
muscle-fibres, but the former derives certain additional support 
from an investigation of the muscles in their most anterior 
region. 
The apices of the ventrally-directed pyramids do not. always 
rest against the vertebral centra, but in some ‘Teleosteans 
(Scomber, Trigla) they originate in the midst of the muscle-mass. 
In this case the pyramids become converted into true cones, and 
in section they appear as a series of concentric circles. In rarer 
instances (Conger) the apices of the dorsal backwardly- directed 
pyramids are also similarly situated, and in a section of the 
dorsal moiety of the lateral muscle two superimposed series of 
concentric circles appear. 
SUMMARY. 
1. The body-wall of a Teleostean fish is composed on either 
side of a series of transverse muscles (myomeres) divided from 
one another by fascie of connective-tissue (myocommata). 
For practical purposes these may be regarded collectively as 
forming a single lateral muscle. 
2. The lateral muscle is composed of a single layer, which 
varies considerably in thickness in different parts of the body. 
3. In its primary condition, such as obtains in the caudal 
region, it is divided into two symmetrical longitudinal moieties, 
which are separated by a horizontal septum passing from beneath 
the lateral line to the vertebral column. 
4. The dorsal moiety is marked externally by a series of back- 
wardly directed >-shaped bands. By joining the apices of these 
>’s an imaginary line is formed dividing the dorsal moiety into 
a (dorsal) mesio-dorsal portion and a ‘(ventr -al) latero-dorsal portion. 
In the mesio-dorsal portion the muscle-fibres run from above 
anteriorly to below posteriorly ; in the latero-dorsal ay they 
take the opposite inclination. 
Internally the mesio-dorsal portion is recognised as a series of 
incomplete hollow pyramids, or cones, whose apices are directed 
posteriorly ; while the latero-dorsal por tion is composed of a series 
of complete hollow pyramids, or cones, whose apices are directed 
forwards. 
The ventral moiety is likewise divided into a (dorsal) latero- 
