VISCERAL ARCHES OF THE GNATROSTOME FISHES. 313 
acquires it, but it later acquires a ventral prolongation which 
extends beyond the branchial diaphragm. According to 
Dohrn the coracobranchialis is formed from the proximal 
portion only of the ventral end of the myotome of each 
arch, and the muscle so formed is not the coracobranchialis of 
Vetter’s descriptions of the adults of other Selachii. Accord- 
ing to Edgeworth the coracobranchialis is formed from the 
entire ventral end of the myotome, and it is identical with 
the muscle described by Vetter. Both authors maintain that 
the coracobranchialis of Vetter’s descriptions is a muscle 
of branchial, and not of spinal origin. 
This comparison of these two embryological works, which 
are the only ones I know of that pretend to give, in detail, 
the development of these several 'muscles, thus certainly 
shows that the published embryological investigations of 
these muscles must be accepted with some reserve. 
The descriptions of the adult may now be considered. 
In the adult Heptanchus the constrictor superficialis of 
each branchial arch is, as described by Vetter (1874), 
practically a continuous muscle-sheet with a large angular 
incisure in its proximal (actually anterior) edge. The dorsal 
attachment, or origin, of the sheet is said to be partly in a 
so-called dorsal superficial fascia, but mainly in thin tendinous 
bands (Platten), which lie external to the musculus trapezium, 
extend to the dorsal edge of that muscle, and represent the 
greatly and progressively reduced posterior portion of the 
superficial fascia above referred to (loc. cit., p. 431). 
The ventral attachment, or insertion, of the sheet is mainly 
in a mid-ventral fascia which lies external and ventral to the 
ventral longitudinal or so-called hypobranchial spinal muscles. 
The large angular incisure in the proximal edge of the sheet 
is made by the articulating ends of the epibranchial and 
ceratobranchial of the arch, and the ends of the muscle 
fibres, on either side of this incisure, are inserted on tho.^e 
two cartilages. The triangular piece so cut out of the con- 
strictor forms the musculus adductor of the arch, but this 
