1869. ] MYOLOGY OF MENOBRANCHUS LATERALIS. 453 
but not its caudal portion, consists of distinct muscular layers super- 
imposed. 
MUSCLES OF THE TRUNK. 
The external oblique (figs. 3, 4, 8,9 & 10, Ex. O). The fibres 
of this muscle extend obliquely backwards and downwards ; and the 
muscle itself forms a sheet of such fibres, which extends from the 
lateral furrow nearly to the ventral middle line of the body, and 
from the shoulder to the pelvis. Towards the tail it seems to unite 
indistinguishably with the internal oblique. 
The internal oblique. This (as in Menopoma) is the largest 
muscle of the body, extending, as one may say, from the urohyal to 
the tail’s end. The fasciculi of fibres are rather large and coarse, 
and extend from one tendinous intersection to another. The direc- 
tion of the fibres is forwards and downwards. The muscle is partly 
inserted into the ilium and its rib ; but some fibres pass beneath these 
hard parts, and the muscle is so continued on into the tail. Towards 
its anterior insertion this muscle appears to fuse with the rectus 
(which is superficial to it), and to constitute a sterno-hyoid (figs. 4 
& 5, S. H). 
The ¢ransversalis is a delicate muscular layer, extending from the 
region of the heart backwards to a little behind the pelvis. 
Rectus (fig. 4, R). This muscle is very delicate and thin in the 
abdominal region ; towards the pectoral arch and in front of it it is 
thicker, and covers externally the internal oblique, with which it 
appears to fuse, when they pass forwards as the sterno-hyoid (figs. 
4 & 5, S. H) to its insertion into the urohyal. This muscle may 
be regarded as continued on even to the mandibular symphysis by 
means of the genio-hyoid (fig. 4, G. 1). 
Retrahentes costarum. ‘The muscular fibres I thus name run 
backwards on each side of the spine, being applied to the under 
surfaces of the bodies and transverse processes of the vertebree. 
They extend from beneath the head to the pelvic region, but do not 
go on into the tail. 
MuscLEs oF THE Heap. 
Temporalis (figs. 1, 2, & 3,7’). This muscle arises from the 
middle of the upper surface of the skull, and (by fascia) from the 
first neural spine, also from the dorsum of the pterygoid and of the 
small bone extending outwards* in front of the suspensorium and 
above the pterygoid. From this extensive origin (reaching forwards 
a little in front of the eyeballs) the fibres converge, and are inserted, 
by a strong tendon, into the summit of the mandible, just in front 
of its articulation with the quadratum. Its insertion is poste- 
rior and somewhat internal to the insertion of the tendon of the 
masseter. 
Pterygoid. 1 do not find this muscle distinct from the temporal. 
* See ‘Ontleed en dierkundige Bijdragen tot de Kennis van Menobranchus, 
by J. Van der Hoeven (Leyden, 1867), pl. ii. fig. 4, 7. 
Proc. Zoou. Soc.—1869, No. XXX. 
