255 

facialis nerves is found, as in Mustelus, Galeus, Seymnus and Prio- 
nodon; and in Seyllium the foramina for the nervi facialis and acusti- 
cus are even separated by a bridge of the dura mater (GEGENBAUR, 
l. c. pp. 46 and 115). In still other selachians the foramina for the 
nervi facialis and acusticus may, as already stated, lie in a fossa that 
is wholly separate and independent of the fossa for the nervus tri- 
geminus, this fossa corresponding to the meatus auditorius internus 
of higher vertebrates. 
The origin of the rectus externus muscle in the acustico-trige- 
mino-facialis recess of Chlamydoselachus would seem, from my 
specimens, to be a specific peculiarity of this fish, but Merritt HAwkKES 
(1906) found what she describes as Division B of this muscle arising 
“from the basis cranii, just anterior to the auditory capsule and 
beneath the foramen for the ganglia for the trigeminal and facial 
nerves, as well as along the proximal part of the optic stalk.’’ And 
the expression “from the basis eranii,” while somewhat indefinite, 
would seem to mean from the ventral surface of the chondrocranium. 
The lateralis and communis portions of the trigemino-facialis 
ganglionic complex of Chlamydoselachus probably lie, in part, in the 
acustico-trigemino-facialis recess, as they do in the corresponding 
recess in Scorpaena (Auuis, 1909, p. 44), but this I have not yet 
attempted to definitely determine. Certainly in those selachians in 
which the ramus ophthalmicus superficialis issues from the recess by 
a separate and independent foramen it would seem as if this must be 
the case. But the larger part of the ganglionic mass, in Chlamydo- 
selachus, lies in a large fossa at the hind end of the orbit, immediately 
ventro-anterior to the base of the postorbital process, and into this 
fossa both the trigeminus and pituitary foramina open. The gang- 
lionie mass is surrounded by tough connective tissue, this tissue also 
partly enveloping the external carotid artery and the internal jugular 
vein. This latter vein runs upward beneath the overhanging post- 
orbital process and then backward dorsal to, and hence morphologi- 
cally lateral to, the hyomandibular, instead of ventro-internal to 
that element as in Amia and teleosts. 
The conditions in the three other selachians that I have examined 
can now be briefly described. 
In Heptanchus cinereus I find the pituitary fossa as described 
by GEGENBAUR, but, related to this fossa, I find a foramen for the 
efferent pseudobranchial artery not shown by GEGENBAUR in either 
