536 
CAPTAIN E. W. SHANN ON 
They will be described in terms of the division of the lateral muscle which were 
advanced in the preceding section, as follows : — - 
(а) Retractor latero-dorsalis pectoralis. 
(б) R. latero-ventralis pectoralis. 
(c) R. mesio-ventralis pectoralis : 
(i) Superior. 
(ii) Medius. 
(iii) Inferior. 
(a) Retractor latero-dorsalis pectoralis ( r.l.d.p .). — I can find no mention of this 
muscle in the works of previous authors. Humphry, whose observations were based 
on Mustelus lasvis, was of opinion that no fibres of the latero-dorsal portion are 
inserted on the tip of the scapula. The latter, he says (51, p. 272), “projects in 
between the fibres of the dorsal muscle, where it terminates in a ligament which is 
lost in one of the transverse septa.” 
After the examination of a considerable number of specimens of Scy Ilium, it still 
remains doubtful whether this muscle may be regarded as present in that form. It 
is usually absent, the tip of the scapula being embedded in a pocket of connective 
tissue ; but in certain cases a few fibres of the latero-dorsal portion undoubtedly took 
origin on the inner aspect of the scapular horn. In the one example of Galeus 
dissected no such fibres were observed. 
It is in the compressed Selachians that this muscle attains considerable develop- 
ment. ■ In Rhina it is well marked in the superficial area, while in the Rays the latero- 
dorsal portion originates in a tendon from the inner aspect of the postero-dorsal angle 
of the scapula. 
In the Rays the outer section of the mesio-dorsal portion (C 2 section in text- 
fig. l) is firmly attached to the postero-ventral aspect of the cartilage which joins 
the scapula to the vertebral column ; while the dorsalmost section (C l) of the mesio- 
dorsal portion runs freely beneath the said cartilage to its attachment on the 
chondrocranium. In these fishes, moreover, there is very little trace of myocommata 
in the anterior region of the lateral muscle, so that the fibres run uninterruptedly in 
longitudinal series. Owen speaks collectively of the whole dorsal moiety of the 
lateral muscle in Batoids (Torpedo), which has been resolved above into its three 
constituent parts, as the “ neuro-medial mass.” 
( b ) Retractor latero-ventralis pectoralis ( r.l.v.p .). Neuro-lateral muscle, Owen ; 
Serratus, Humphry ; Latero-scapularis, Gegenbaur. — Humphry observed in Mustelus 
that the scapula lies upon the latero-ventral portion, its lower edge being connected 
with one of the transverse septa of this muscle ; moreover, that some of the fibres of 
the muscle pass into its under surface, constituting a “ serratus.” 
In Scyllium, Galeus, and Acanthias, the superficial fibres of the latero-ventral 
portion are attached to the posterior border of the scapula, while a few of the deeper 
