680 ALLTS, [Vou exIt; 
Vetter is, therefore, probably wrong. Between Tiesing and 
Fiirbringer there is no way to choose. The innervation given 
by Tiesing seems more natural, and if he be right the muscles 
in selachians can be readily homologized with those in Amia. 
If Firbringer is right no comparison seems possible. I there- 
fore assume Tiesing to be correct. 
In Amia there are, belonging to each of the first three bran- 
chial arches, two dorsal muscles and two dorsal ligaments. 
One of the two muscles of each arch arises from the side of 
the skull, and is inserted on the infrapharyngobranchial of the 
arch next following the arch to which the muscle belongs, the 
large so-called third infrapharyngobranchial being here con- 
sidered as the fused third and fourth infrapharyngobranchials. 
The other muscle, on each arch, arises with the first muscle 
from the side of the skull, and is inserted on the epibranchial 
of its ownarch. That the muscles belong, in each case, to the 
arches to which they are assigned is shown conclusively by the 
innervation. The two dorsal ligaments on each arch are, 
one, the articular ligament connecting the epibranchial of its 
arch with the infrapharyngobranchial of the next following 
arch, and the other, the interarcual ligament connecting the 
epibranchial of its arch with the infrapharyngobranchial, or 
epibranchial, of the next following arch. Between these two 
ligaments, that is, immediately median to the interarcual liga- 
ment, the ramus pharyngeus of the next following arch always 
passes downward to reach its destination. 
If, now, muscles I and II in Acanthias should acquire at 
their upper, anterior ends, an attachment to the side of the 
skull, and muscle III should become a ligament, an arrange- 
ment of muscles and nerves would arise so closely resembling 
that found on the first three arches of Amia, that the muscles 
in the two fishes can safely be considered homologous. Muscle 
I, on each of the first three arches of Acanthias, is thus, in all 
probability, the homologue of the internal levator of the corre- 
sponding arch in Amia, the muscles of the second and third 
arches, in Amia, being united to form a single muscle, the 
levator arc. branch. int. posterior, the largest of all the levator 
muscles. Muscle II, on each arch of Acanthias, is the homo- 

