546 
CAPTATN E. W. SHANN ON 
(ii) Adductor profundus (add.p.). 
Arises from the proximal cartilages of the fin and is inserted into the distal 
radials and the horny fin-rays (ceratotriehia): Bratjs (9) maintains that the 
adductor is inserted only into the horny rays, never into the radials ; but my 
observations do not confirm this statement. The same author has described in great 
detail the musculature and innervation of the pectoral fin of Acanthias (op. cit., 
Taf. xii, fig. l), and he shows very clearly the remarkable fact that the muscle 
bundles correspond neither in number nor' position with the distal radial cartilages. 
(2) Abductor (ventral or outer) Musculature. 
The abductor muscle is in most points the counterpart of its antagonist the 
addmctor, though the number of component muscle bundles is not necessarily the 
same. It may with equaA justice- be divided into two layers, abductor superficialis 
(abd.s.) and abductor profundus (abd.p.). 
(i) Abductor superficialis (abd.s.). 
Arises from the coracoid and is inserted into the abductor profundus. The first 
three preaxial bundles, which are inserted on the ventral aspect of the propterygium, 
show no division into layers, and may be regarded as belonging entirely to the 
superficial layer ; they are best seen from the lateral aspect. The fourth superficial 
bundle, also lateral in position, has a double insertion, its deepest fibres being 
inserted into the proximal border of the mesopterygium, while its superficial fibres 
are inserted into the proximal portion of the propterygial radial and into the fascia 
covering the first bundle of the abd.p. A similar arrangement will be noted in two 
of the superficial bundles in Chimsera. The first four bundles serve as depressors of 
the propterygium and its radial. The remaining twenty bundles are visible from 
the ventral aspect and are inserted in the typical manner. 
(ii) Abductor profundus (abd.p.). 
Arises from the metapterygium and is inserted into the distal radials and the 
ceratotriehia. There is a small muscle which, arising from the outer portion of the 
mesopterygium, is inserted into the most preaxial horny rays ; this must be regarded 
as the first (preaxial) deep bundle, and corresponds with the fourth bundle of the 
superficial series. The second bundle of the abductor profundus is inserted into all 
the remaining ceratotriehia articulating with the propterygial radial. 
The above description of the abductor musculature applies to Scy Ilium, and 
lack of time has ^rendered impossible anything but a superficial examination of 
the other types. So far as my observations go, they indicate that the condition 
of the musculature in Scyllium is typical of the general arrangement in Selachian 
fishes. 
