No. 3.] WUSCLES AND NERVES IN AMIA CALVA. 617 
The next or third branch of the mandibularis externus, in 
the adult used for illustration, was given off just before the 
internus separated from that nerve. It ran almost directly 
downward and entered the preoperculum opposite organ 13, 
sending a branch to that organ and then continuing downward 
in the bone to organs 12 and 11. Before entering the bone a 
branch was sent outward and downward through the adductor 
mandibulae and then outward and downward along the outer 
surface of that muscle. It separated into two portions and 
supplied the pit organs of the vertical cheek-line and mandib- 
ular line, the branch to the latter crossing superficially the 
branches of the fourth branch of the trigeminus, where they 
turn inward at the lower corner of the adductor. In 35 mm. 
specimens, and in most adult specimens also, there were two 
branches arising from the externus after the internus had sepa- 
rated from it, one branch going to organ 13 and one to organs 
12 and 11, the branch to the cheek-line arising between the 
other two, or as a branch of the one to organs 12 and 11. 
After giving off the branch to organs 12 and 11 the externus 
passes under the cartilaginous posterior corner of the palato- 
quadrate arch, and then under the preoperculum into the canal 
between that bone and the symplectic. From that canal it 
issues at about the middle of the hind edge of the symplectic, 
between that bone and the preoperculum, and, turning slightly 
backward, passes external to the ligamentum mandibulo-hyoi- 
deum, then downward and forward around the ventral surface 
of that ligament into a groove on the median surface of ossicle 
a.’ Tt then continues forward in that groove, and in a pro- 
longation of the groove on the median surface of the ventral 
thickened part of the articular, the nerve being here covered 
internally by the lower edge of the splenial. 
While passing downward along the external surface of the 
ligamentum mandibulo-hyoideum a branch is sent forward to 
organ 10 operculo-mandibular, the branch entering the articular 
along its hind edge lateral to the articular process for the sym- 
plectic. This branch seems to have been mistaken by van 
Wijhe for the main r. mandibularis internus (No. 129, p. 292). 
The next branch of the externus, that to organ No. 9, is given 
