CRANIAL NERVES OF SIREN LACERTINA 275 
quent course will be noticed in connection with the latter nerve. 
The ventral (md.4b) of the two branches from the ramulus mandi- 
bularis externus passes along the ventral border of the masseter 
muscle and gives off a branch which passes almost directly dor- 
sally through the muscle to join the dorsal branch, as above stated, 
on the dorsal border of the tendon of the masseter muscle. The 
rest of the branch runs anteriorly along the ventral border of the 
muscle and anteriorly to the latter, and, passing dorsally around 
the angle of the mouth, is distributed to the skin of the upper lip 
(figs. 8-6). The remainder of the ramus mandibularis with its 
branches supplies the skin of the lower jaw and to some extent 
the mucous membrane of the mouth. 
The two small muscles having their insertion on the antorbital 
cartilage in Siren appear to correspond to the two muscles in 
Amphiuma designated by the writer as levator and retractor 
bulbi. In Amphiuma the movements of the antorbital cartilage, 
to which the muscles in question are attached, seem to have def- 
inite relation to the position of the eyeball. The levator bulbi 
muscle raises the cartilage, pushing the eyeball dorsally and later- 
ally; the retractor bulbi muscle pulls the cartilage ventrally and 
posteriorly allowing the eyeball to sink in. In Siren the antorb- 
ital cartilage appears to have no direct relation to the movements 
of the eyeball. It extends laterally from its attachment to the 
orbito-sphenoid around the posterior border of the internal naris, 
then curves anteriorly along the lateral border of the opening, 
tapering into a sharp point (figs. 7-9, 15, ao.). One muscle 
(rtao.) which corresponds to the retractor bulbi in Amphiuma, 
has its origin on the orbito-sphenoid bone (in Amphiuma on the 
pterygoid cartilage and maxilla) and, running anteriorly, is in- 
serted on the ventro-lateral border of the antorbital cartilage. 
As in Amphiuma, its action is to pull the cartilage posteriorly 
and ventrally. This movement, from the relation of the cartilage 
to the lateral valvular fold of the postnares, will open the nostril. 
The other muscle (lvao.), which has its origin on the side of the 
orbito-sphenoid (as in Amphiuma) and its insertion on the postero- 
dorsal part of the antorbital cartilage, by its contraction raises 
the latter and pulls it somewhat anteriorly, thus closing the in- 
