No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 677 
6. Review and Comparison. 
In the primitive condition of all fishes there was, according 
to Vetter (No. 124, pp. 443-446), a single, annular, general 
constrictor muscle, which later separated into two layers, an 
outer and an inner one. From the outer layer arose the inter- 
branchial muscles of the visceral arches ; from the inner one 
the adductor and interarcual muscles, and the constrictor of 
the pharynx. Connected with the primitive general constrictor 
there were a large number of visceral arches all lying “ ober- 
flachlich in der diinnen Leibeswand,” their upper ends im- 
bedded in and moved by the “Ringmusculatur des Schlundes.” 
Whether the arches so described lay inside or outside the 
muscle is not clear either in this statement of Vetter’s conclu- 
sions, taken alone, or taken in connection with further state- 
ments made in two footnotes. The arches would seem to lie 
inside the muscle were it not that Vetter definitely states his 
acceptance of Gegenbaur’s conclusion that the adductor man- 
dibulae muscle, which is considered as the serial homologue of 
the adductor muscles of the branchial arches, lay primarily on 
the inner surface of its arch. 
In Acipenser and all teleosts Vetter concludes (No. 125, pp. 
485 and 534) that the adductor muscles of the visceral arches 
become greatly reduced, and that they may, on certain or on 
all of the arches, disappear entirely. The interarcuales also 
disappear, or may possibly give origin to the third, fourth, and 
fifth levatores arch. branch. in Acipenser and to the obliqui- 
dorsales in teleosts (No. 125, pp. 485 and 534). The inter- 
branchiales give origin to the levatores arc. branch. ext. and 
int. of teleosts and to the interarcuales ventrales and levatores 
arc. branch. (at least the first two) in Acipenser. The trans- 
versi dorsales are said to be entirely new formations, or to be 
derived, possibly, from the retractores; the retractores them- 
selves are possibly the homologues of the subspinalis of Acan- 
thias and Heptanchus. 
With these general conclusions of Vetter I do not entirely 
agree. The arrangement and innervation of the muscles in 
Amia seem to me to strongly indicate that they all lay primarily 
