VISCERAL ARCHES OF THE GNATHOSTOME FISHKS. 391 
or near the morphologically external but actually posterior 
edge of the cartilaginous bar of the arch. The posterior 
efferent, artery, also, was not affected by this change in 
position of the constrictor muscle, but it later underwent 
reduction or abortion in its ventral portion, while dorsally it 
persisted and retained its normal position posterior to the 
spiracular cartilage, that cartilage representing either the 
dorsal extrabranchial of the arch or one or more of the 
branchial rays. That any of the branchial rays of this arch 
could, in such a shifting of the constrictor, have acquired the 
positions of the labial cartilages seems quite impossible. 
The long musculus constrictor superficialis, having acquired 
this position on the anterior (lateral) surface of the carti- 
laginous bar of its arch, was later more or less completely 
cut in two at the places where it crossed the palatoquadrate 
and the mandibula. The portion so cut out of the middle of 
the constrictor was then added to the small, pre-existing' 
musculus adductor to form the large and powerful adductor 
of the adults of living fishes, while the ventral portion formed 
the intermandibularis and the dorsal portion the levator of 
the arch. Certain of the fibres of the original constrictor 
were, however, quite certainly not thus cut through at tlie 
places where they crossed the palatoquadrate and mandibula, 
for certain of them still extend, in the adults of living fishes, 
the full length of the arch. This is markedly the case in 
certain of the fibres of the musculus spiracularis of Astrape. 
This muscle is said by Luther (1909, p. 14) to be developed 
from the posterior fibres of the dorsal portion of the primitive 
constrictor of the arch and to have a ventral prolongation 
which lies along the internal surface of the mandibula 
(kieferapparat) and extends as far as the symphysis of the 
mandibulse, there uniting with its fellow of the opposite 
side. This ventral prolongation is a feeble muscle, of no 
apparent functional importance, and certainly cannot be a 
secondary formation, as Luther considers it to be. It 
must, on the contrary, represent a persisting remnant of a 
distal part of the primitive constrictor which, when the 
