66 
In Esox I find the extrascapular as a delicate Y-shaped bone, 
to which CoLLinGE (No. 13) has already referred, and the related con- 
ditions of the sensory canals deserve especial attention. The parietals 
in this fish are, as is well known, relatively small bones lying on 
either side of a median supraoccipital. They largely cover the dorsal 
surface of the epiotics (exoccipitalia), which lie immediately beneath 
and behind them, and these latter bones adjoin the supraoccipital an- 
tero-mesially, and laterally form the mesial wall of the supratemporal 
hole. What seems unquestionably the homologue of the middle head 
line of pit organs of Amia lies, on each side of the head, immediately 
superficial to the parietal, and the line is so strongly developed that. 
it forms a marked groove on the outer surface of the dermis. The 
line begins, laterally, directly dorsal to the dorsal end of the pre- 
operculo-mandibular canal, and its mesial end almost meets the corre- 
sponding end of its fellow of the opposite side. The ends of both 
lines here slightly overlap the antero-lateral edges of a large round 
median scale which lies directly superficial to the supraoccipital bone. 
Elsewhere the two lines lie anterior to the scales of the trunk. The 
innervation of this line I have not yet determined, but it must be 
the middle head line of pit organs of the animal, not only its position 
indicating this but also the fact that there is a short supratemporal 
commissure lying in the extrascapular bone of the fish. This latter 
canal lies posterior to several rows of scales. On the dorsal surface 
of the parietal, beneath the line of pit organs, there is a well marked, 
depressed line, or groove, which indicates its course and position. 
There thus seem to be, in Teleosts, two groups differing consi- 
derably from each other in the relative importance of the middle head 
line of pit organs and the supratemporal canal line. The bony and 
cartilaginous Ganoids may also be found to differ from each other in 
this same respect; and it is the cartilaginous Ganoids, and the Teleosts 
represented by Esox, that seem to present the conditions that most 
resemble those found in the Stegocephali, the only animals above 
fishes, so far as I can find, in which lateral sensory canals are de- 
scribed. The so-called canals in these latter animals may, however, 
be simply pit lines, similar to the supratemporal line in Esox, for, 
as already once stated above, Frirscu says of them that they are 
found as half cylindrical gutters on the external surface of the bones 
to which they are related, and that they increase in depth and distinct- 
ness with the age of the fish. If they be simply highly developed pit 
lines, as thus seems possible, the Stegocephali would not differ so 
radically, in this respect, from all other known Amphibia. 
