4098 ALLIS. [Vou. XII. 
The common carotid artery, soon after its origin from the 
first aortic arch, and just before reaching the lateral wing of 
the parasphenoid, separates into two parts, the internal and 
external carotids. 
The internal carotid (zc) enters the palatine canal between 
the parasphenoid and the basis cranii, and after crossing the 
palatine foramen, turns upward into the internal carotid canal, 
and enters the cranial cavity under, or median to and in front 
of, the optic nerve of its own side. As it leaves the palatine 
canal a small branch is sent forward in that canal, and as it 
traverses the internal carotid canal another small branch is 
sent outward and forward in the small branch canal to join 
the efferent pseudobranchial artery, as already described on 
page 493. 
Having entered the cranial cavity, the internal carotid artery, 
in the adult, turns backward and then outward and forward 
under the optic nerve. At this point it separates into three 
parts, an optic, an anterior or olfactory, and a posterior portion. 
The optic portion runs outward with the optic nerve, enclosed 
in the membranous sheath enclosing the nerve, and supplies, 
according to Wright, the ventral half of the choroid gland. 
The olfactory portion runs directly backward to about the level 
of the hypophysis, where it separates into two parts, both of 
which turn inward and then forward above the optic nerve and 
supply the anterior parts of the brain and brain cavity, one 
of the branches running forward under the olfactory nerve 
toward the nasal sack. The third, or posterior, portion of the 
artery runs at first directly backward, median to the olfactory 
portion. Reaching the level of the auditory labyrinth, it gives 
off a large branch, and, turning inward behind the lobus infe- 
rioris, joins its fellow of the opposite side, thus forming a cir- 
culus cephalicus, from the median point of which a branch is 
sent forward and another backward under the brain. 
In embryos the optic chiasma lies in front of the internal 
carotid canal; and the internal carotid artery, after issuing from 
its canal, runs upward and forward along the lining membrane 
of the optic fenestra, behind the optic nerve. In this part of its 
course it becomes so flat and thin that I could not definitely 
