506 ALES. ivion. xin 
formed around the saccus vasculosus into which the rectus 
externus on each side has crept, following the vein vo or the 
nervus abducens, and the orbital opening of the canal is the 
fused foramen of those two structures, or, as in Amia, of those 
two foramen and the foramen of the trochlearis, oculomotorius, 
and profundus as well. That a muscle should enter the canal 
of its nerve certainly seems more natural than that it should 
enter one serving simply for the passage of a lymph canal. 
In Mustelus, where there is no eye-muscle canal, the rectus 
externus arises (No. 123, p. 81) close to the opening of the 
canal for the abducens. In larvae of Axolotl (No. 117, p. 16) 
the side wall of the skull is pierced, behind the optic foramen, 
by a larger opening, which is in part filled with muscle 
«Anlagen.”” Through this opening pass also a blood-vessel 
and a bundle of nerve fibres. 
Although no trace of a transverse lymph sinus was found 
in the eye-muscle canal, such a sinus was always found, in 
larvae, extending from orbit to orbit between the internal 
carotid canals and the optic chiasma, and connecting the 
periorbital lymph spaces. This sinus is represented in the 
adult by the interorbital groove already described on page 406, 
but whether there is a transverse lymph passage at this point 
in the adult or not I did not determine, as my attention was 
not called to the point in the earlier stages of this work, and 
lately I have had no material suitable for its investigation. 
The groove is, however, certainly the canalis transversus of 
selachians, and Gegenbaur’s description of the canal in Galeus 
and Squatina (No. 44, p. 76) could almost be taken for that in 
Amia, the “ Sattellehne” in the former being considered as the 
posterior edge of the transverse Wulst or bar in the latter. 
The carotid canal or canals, however, lie in selachians in front 
of instead of behind the canalis transversus. The presence of 
this latter canal, together with an eye-muscle canal in Amia, 
shows definitely that the latter is not derived from the former 
as Gegenbaur (No. 44, p. 78) and Sagemehl (No. 104, p. 217) 
were led to suggest. 
