150 EDWARD PHELPS ALLIS, JR. 
mens I have examined, from behind mesially and more or less 
~ aborally, apparently tending to become approximately parallel 
to the upper edge of the mouth. 
Neither the line of the external apertures of the adult nor the 
line of the median raphe of the Schneiderian membrane thus lies 
in the direction of the nasal groove of embryos, this apparently 
having been caused by, or being related to, a change in direction 
of the long axis of the external opening of the nasal pit. The 
descriptions and figures of embryos do not permit the several 
stages in this change in direction of this axis to be followed, 
but that there is such a change, and that it has the character of 
a partial rotation of the axis of the opening in the plane of that 
opening is evident from a comparison of the conditions shown by 
Berliner (02) in embryos of Acanthias with those found in the 
adult of that fish; the central line of the opening of the nasal 
pit of embryos, and the line of the median raphe of the 
Schneiderian membrane, both lying approximately in the line of 
the nasal groove and hence directed from in front orally and 
mesially, while in the adult the long axis of the fenestra nasalis 
and the line of the median raphe are directed aborally and 
mesially, the line of the external apertures crossing this line at a 
considerable angle and being directed mesially. The appearance 
is accordingly that of the long axis of the fenestra nasalis having 
rotated from left to right through a considerable angle, carrying 
the median raphe with it and dragging, at either end, the related 
external aperture a certain distance from its embryonic position. 
The rotation of the nasal apertures is accordingly less extensive 
than that of the axis of the fenestra, and the passage from each 
aperture into the nasal capsule is, in consequence, pulled out and 
lengthened to a variable extent, the two passages being directed 
in opposite directions. 
In the adult Mustelus (probably vulgaris) the long axis of the 
fenestra nasalis extends from in front orally and laterally, lying 
approximately parallel to the upper edge of the mouth and 
coinciding in direction with the line of the median raphe of the 
Schneiderian membrane (figs. 8 and 9). The line of the centers of _ 
the external nasal apertures crosses this line at a considerable an- 
