552 DAVIDSON BLACK 
(R. mand. V); (c) m. levator arcus palatini (R. mand. V); (d) 
m. levator operculi (R. opere. VII). In expiration:® (a) m. 
adductor operculi (R. opere. VII); (b) m. adductor arcus pala- 
tini (R. mand. V); (c) m. adductor hyomandibularis (R. opere. 
VII); (d) m. geniohyoideus (R. mand. V.+R. opere. VII). 
The action of the opercular apparatus is reinforced to a vari- 
able though usually slight extent by the intrinsic branchial 
musculature as follows. In inspiration: (a) mm. interarcuales 
ventrales (both oblique and transverse group) (Rr. branch. [X— 
X); mm. interarcuales dorsales (Rr. pharyng. X). In expira- 
tion: (a) mm. levatores arcum branchialium externi et interni 
(Rr. branch. [X—X); (b) m. hyohyoideus (R. opere. VII). 
In addition to the opercular and branchial respiratory mechan- 
ism, the branchiostegal apparatus may play a most important 
role in the production of the respiratory current in certain marine 
forms (e.g., Lophius). Borcea (11) has pointed out that the 
development of the branchiostegal apparatus and its muscula- 
ture (m. hyohyoideus and special adductors and abductors) 
occurs in inverse ratio to the development of the opercular 
mechanism. Baglioni (8), carrying this investigation further, 
has arranged teleosts into groups depending upon the type of 
their respiratory mechanism. Of these groups it will only be 
necessary to mention three in the present connection, viz., 
(1) those in which the branchiostegal apparatus is practically 
wanting (e.g., Conger); (2) those in which both branchiostegal 
and opercular mechanisms are more or less equally well repre- 
sented (e.g., Pleuronectidae); and (3) those in which practically 
15 The m. geniohyoideus, whose action was considered to be inspiratory by 
Deganello and others, has been shown by Holmquist (46) to be chiefly an ex- 
piratory muscle. On account of its action, as well as for other reasons, the 
muscle has been termed by this investigator the m. protractor hyoidei. 
16 The extent to which the fibers of the facial nerve contribute to the innerva- 
tion of this muscle is subject to some question. In Ameiurus few. motor VII 
fibers can reach the geniohyoideus owing to the very slight anastomosis between 
the mandibular V and opercular VII branches (Herrick, 36). The anastomosis 
between these nerves seems to be more extensive, however, in Gadus (35) where 
the condition resembles that obtaining in Amia (1), but in Menidia (34) the m. 
geniohyoideus is supplied wholly by motor trigeminal branches. 
