455 
along both the anterior and posterior edges of those bones, In this 
tissue are found the larger part, but not all, of the external openings 
of the lateral canals. 
The upper and lower lips of the fish, excepting only at the an- 
terior ends of the jaws, are formed, respectively, by the folding up- 
ward or downward upon itself of a thick fold of the tough dermal 
tissue above referred to, the free edge of the lateral portions” of the 
upper lip thus being di- 
rected upward and that of PMX ana i’s’p 
the lower lip downward. TERN 
This might be otherwise pmp! 
described by saying that ; 
a deep furrow extends down- 
ward into the upper lip, 
and upward into the lower 
lip, the furrow extending 
from the hind end of the 
mouth forward nearly to 
its anterior end, and there 
vanishing. In the upper lip 
the anterior end of the 
furrow lies opposite and 
against the anterior edge 
Fig. 1. Side view of the 
skull of a 44-cm specimen of 
Polypterus bichir, showing the 
lateral sensory canals and the 
positions of the sensory organs in 
these canals, The bone Y” of 
TRAQUAIR’s descriptions has been 
removed, 
of the base of the nasal tube of the fish. These folded portions of 
the lips occupy depressed regions on the outer surfaces of the jaws, 
this being more marked in my 30-cm specimens than in the older ones. 
The Main Infraorbital Canal of Polypterus, using the same 
descriptive terms I have heretofore employed, begins in the median 
line, on the top of the snout, as a direct continuation of its fellow of 
the opposite side. It here lies in the bone described by both Traquair 
and PoOLLARD as the median ethmoid. Running laterally, downward, 
‚and slightly forward the canal leaves the ethmoid and enters the pre- 
maxillary, giving off as it passes from one bone to the other, or just 
as it enters the premaxillary, the first tube actually found in the line. 
28* 
