61 
ristische Vorsprünge, zwischen welchen sich vier von Muskeln erfüllte 
Gruben befinden; das Verhältnis dieser Vorsprünge zu den Gruben 
bietet einen unendlichen Wechsel dar”. 
In Amia the exoccipitale is not traversed by any part of the 
lateral sensory canals. It lies, however, directly internal to the extra- 
scapular, which bone lodges the supratemporal crosscommissure of 
the lateral system. In Teleosts, also, the bone is never, so far as I 
can find, traversed by a lateral canal, and, although not always lying 
directly internal to the extrascapular, as in Amia, it seems to lie 
internal to the mesial end of that bone, or internal to the mesial end 
of the lateral canal that traverses the bone, the canal naturally ex- 
tending slightly beyond the end of the bone that lodges it. The ex- 
occipitale of Amia and Teleosts thus seems to have much the same 
relations to the extrascapular and to the supratemporal commissure 
of the lateral canals, that the primary part of the squamosal has to 
the dermal part of that bone and to that section of the main infra- 
orbital canal by which it is traversed, and that the postorbital ossi- 
fication of my descriptions of Amia has to the dermal postfrontal and 
to the section of canal it lodges. The dermal postfrontal, it is also 
to be noted, often does not directly overlie the primary ossification 
to which it is considered to be related. 
According to VROLIK, the exoceipitale of Teleosts is usually tra- 
versed by, or partly encloses, a part of the posterior semicircular 
canal of the ear; but in certain Teleosts it simply lies, as it does in 
Amia, external to the summit of that canal, but wholly separated from 
it by cartilage. As the squamosal and postorbital ossifications are 
similarly related, respectively, to the external, and anterior semicircular 
canals, the relations of dermal canal components to primary ones, in 
the three otic regions, may be something more than a simple coin- 
cidence. 
The extrascapular of Amia is a large dermal plate that lies in 
a transverse position superficial to the exoccipitale, and meets, in the 
middle line of the head, its fellow of the opposite side. The lateral 
part of the bone is traversed by the main infraorbital canal of the 
lateral sensory system, and it lodges one sense organ of that line. 
From this section of canal the supratemporal crosscommissure arises, 
and, traversing the bone, unites with its fellow of the opposite side 
of the head. The commissure contains three sensory organs on each 
side. 
In Teleosts, the extrascapular is, according to SAGEMEHL (No. 27, 
p. 181), almost always found as a superficial dermal bone, usually 
but little developed, lying between the arms (“Zinken”) of the supra- 
