No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 525 
dog, where the muscle is also found, he finds the lower portion 
of it innervated by a similar branch given off close to the branch 
to the rectus inferior (No. 113, pp. 218 and 220). This inner- 
vation of the retractor bulbi does not agree with that given by 
others. Wiedersheim says (No. 128, p. 339) that it is inner- 
vated by the abducens. Huxley says (No. 60, pp. 67 and 74) 
that in all vertebrates “‘the muscles of the nictitating mem- 
brane, and the retractor bulbi, or musculus choanoides, when 
such muscles exist,” are innervated by the abducens, and that 
the musculus choanoides when it exists ‘lies within the four 
recti, and is attached to the circumference of the posterior 
moiety of the ball of the eye.’” Mivart also (No. 81), in the cat, 
gives the innervation of the choanoid muscle by the abducens, 
and Hoffmann (No. 56, p. 209) says that in Lacerta the rectus 
externus and retractor bulbi develop from the same somite. 
Schwalbe’s statement may, therefore, be considered as due to 
some error in observation. It, however, finds some support by 
what Herrick finds in Amblystoma, for after stating (No. 55, p. 
200) that the abducens separates peripherally into two branches, 
one of which goes to the retractor bulbi, he adds, “ Although 
the two branches of the sixth nerve are indistinguishably blended 
when they leave the Gasserian ganglion, yet it would seem that 
the branch destined for the m. retractor bulbi ought not to be 
assigned to this nerve, but to the trigeminus.”” Herrick further 
states that, in Salamandra maculata the retractor is innervated 
by the oculomotorius, the statement being probably made on 
the authority of von Plessen and Rabinovicz (No. 92, p. 7). 
In reptiles, birds, and higher vertebrates the six muscles of 
the eyeball are, according to Schwalbe, innervated as in Anura, 
for in speaking of the latter he says: ‘‘Das Innervationsschema 
der Augenmuskeln der Anuren weicht in nichts von dem 
bekannten der hdheren Wirbelthiere ab.” In these higher 
forms there may be a musculus choanoides, as already stated, 
and there is usually a levator palpebrae superioris, innervated, 
according to Schwalbe, when it exists, by a branch of the 
superior division of the oculomotorius. 
It is thus evident that the muscles of the eye in vertebrates, 
although performing similar functions, are not homologous 
