548 
CAPTAIN E. W. SHANN ON 
This and the muscle next to be described are figured by Vetter (88, Taf. xii, 
fig. l), but erroneously, for they are represented as parts of one and the same muscle 
sheet, whereas they are in reality divided very distinctly by the lateral line ; more- 
over, their fibres take different directions. ' 
( b ) Retractor latero-ventralis pectoralis ( r.l.v.p .). — Two straps of muscle (fig. 12) 
are given off from the latero-ventral portion of the lateral muscle, one of which 
(externus) is inserted on the outer aspect of the scapula, while the other (internus) 
is inserted on its inner aspect. 
(i) R.l.v.p. externus. 
In Chim sera this muscle is covered to such an extent by the elevator muscle of 
the propterygial radial and the r.m.v.p.sup. that it is scarcely visible until the latter 
are reflected ; in Callorhynchus, on the other hand, where the first of these muscles 
is wanting and the second is much more limited in extent, a large tract of the 
r.l.v.p.ext. in the region of its insertion is visible without dissection. Inserted by a 
broad tendon in a slight groove on the outer aspect of the scapula, and extending 
a short distance above the level of the lateral line, the muscle fibres run obliquely, 
especially in Callorhynchus, downwards. 
(ii) R.l.v.p. internus. 
This muscle lies slightly ventral as well as internal to the foregoing in Chimeera, 
but in Callorhynchus is directly beneath it. Taking origin from the latero-ventral 
mass, its fibres pass, gently downwards in Chimsera, parallel to the major body-axis 
in Callorhynchus, to their insertion on the inner aspect of the scapula. 
(c) Retractor mesio-ventralis pectoralis ( r.m.v.p .). — As in the Selachians, the 
mesio-ventral portion of the lateral muscle is attached by three tolerably distinct 
areas of insertion to the girdle ; but, except in Callorhynchus, it shows no tendency 
to spread upon the fin muscles. The entire mesio-ventral portion is intercepted at 
the pectoral girdle. 
(i) R.m.v.p. superior. 
In Chimsera this is an extensive sheet of muscle, whose fibres, arising from the 
fascia covering the lateral muscle, immediately below the lateral line, run obliquely 
downwards and forwards to their insertion on the posterior rim of the scapula. The 
dorsal fibres take origin from the fascia covering the surface of the latero-ventral 
portion, and for 20 mm. extend as far as the lateral line, this extent beginning 
.19 mm. behind the scapula; thenceforward the end-line bends downwards, arc-wise, 
and the ventral fibres gradually fuse with the latero-ventral portion and the middle 
section of the mesio-ventral portion. It is no longer recognised as a girdle muscle, 
but as the upper section of the mesio-ventral portion of the lateral muscle. Ventrally, 
the muscle is separated by a distinct fascia from the r.m.v.p.med. 
Callorhynchus differs from Chimsera in that the r.m.v.p.sup. is continuous ven- 
