1905. ] ARTERIAL SYSTEM IN SAUROPSIDA. 63 
basilar artery are the posterior cerebellar, and these arise a little 
behind the middle of the medulla. The two arteries are perfectly 
syminetrical with each other as to their point of origin. They 
are, however, different in their branching. The right artery 
gives off, shortly after its origin from the basilar, a strong artery 
running backwards along the side of the spinal cord. This 
branch exists and pursues the same course on the left side; but 
on that side of the brain it arises separately from the basilar 
artery. Between the origin of the posterior cerebellar arteries and 
the bifurcation of the basilar anteriorly are three pais of small 
arteries supplying adjacent regions of the medulla. A slightly 
larger artery, which is the anterior cerebellar, arises from the 
fork of the basilar. This fork is U-shaped in the Teguexin (text- 
fig. 18, p. 65), and not V-shaped as in the other Lizards described 
here. The U-shape is due to the fact that the two carotids run 
parallel to and almost in contact with each other for some distance 
before they join the circle of Willis. The carotids, moreover, lie 
within the area bounded by the third nerves very close to and about 
ona level with those nerves. Theartery formed by the junction of 
the basilar and carotid on each side, often spoken of merely as the 
carotid, passes outwards and slightly backwards at first, when it is 
practically at right angles with the basilar. In this region the 
artery shows different relations on the two sides of the body. On 
the left side it runs in front of the third nerve; on the right side 
it lies behind that nerve. The first branch arising after the 
carotid is at the bend of the artery, where it turns forward ; this 
very stout artery supplies the cerebellum and optic lobe; im- 
mediately in front of this is the artery of the optic lobe. This 
state of affairs occurred on the left side of the body; on the right side 
the two arteries arose by a common trunk. On both sides the 
artery of the corpus bigeminum gives off an artery to the cerebral 
hemisphere which buries itself in the furrow between the hemi- 
sphere and the optic lobe. From the inner side of the circle of 
Willis, just opposite to the bigeminal artery on the left side and to 
the conjoined arteries just mentioned on the right side, arises an 
artery which runs to the optic chiasma. This artery is precisely 
like that of other Lacertilia. The next artery to be given off is 
the posterior cerebral, which plunges at once into the furrow lying 
between the optic lobe and the cerebral hemisphere. The middle 
cerebral artery, which is the largest of the cerebral arteries, runs 
in the usual way along the Sylvian depression, and just in front 
of the point of origin of this the circle of Willis practically ends 
in the strong ophthalmic arteries which follow the optic nerves. 
There are therefore no differences of importance between the 
arterial system of the brain of Zupinambis and of the other 
genera of Lizards reported upon in the present communication. 
§ Cerebral Arteries in the Lacertilia. 
We may deduce from the facts just described the chief 
