294 EDWARD PHELPS ALLIS, JR. 
verses the sinus cavernosus of man was the homologue of the 
vena jugularis of fishes; that the intercavernous sinuses repre- 
sented the pituitary veins of fishes; and that the cavernous and 
intercavernous sinuses and the cava Meckelii_ together 
represented the myodome of Amia together with its so-called 
upper lateral, or trigemino-facialis chamber. This is, how- 
ever, an error, for the so-called cavernous and intercavernous 
sinuses together represent a dorsal myodomic cavity plus 
the internal carotid canals, and the venous vessels tra- 
versing this cavity are, together, the homologues simply of 
the pituitary veins of fishes. The cavum Meckelii is then sim- 
ply a trigeminus recess and not a trigemino-facialis chamber. 
In Thane’s figure (94, fig. 405, p. 523) of a transverse sec- 
tion through the sinus cavernosus of the adult man, the outer 
wall of the sinus, formed by the dura mater, is thickened and 
is traversed by the oculomotorius, trochlearis, profundus (first 
branch of the trigeminus), abducens and maxillaris trigemini 
nerves. The inner wall of the sinus is continued across the dor- 
sal surface of the sella turcica, and is there separated by a nar- 
row space from the membranous pituitary sac, this space being 
traversed, on either side of that sac, by the intercavernous 
sinuses. The internal carotid artery enters this sinus through 
the inner part of the foramen lacerum, runs forward in the carotid 
groove on the lateral surface of the body of the sphenoid, and 
turns upward in a semicircular notch on the posterior surface of 
the preclinoid wall, this notch representing a remnant of the 
internal carotid canal of Amia. The artery lies lateral to the 
pituitary vein, but if the myodomic cavity were convex on its 
ventral surface, as it is in fishes, instead of concave, as in man, 
the artery would lie ventral and internal to the loop formed by 
the veins of opposite sides, as it does in fishes. The external 
carotid artery lies everywhere external to the cranial wall, as 
does also the vena jugularis externa, terminal branches only 
being sent into the cranial cavity. 
The relations of the veins and arteries of man to the crania 
wall are thus, like those of the nerves, strictly similar to those 
in the hypothetical piscine cranium here under consideration, 
