1905. ] ARTERIAL SYSTEM IN SAUROPSIDA. 61 
§ Brain of Tropidurus hispidus. 
In comparing the arterial system of the brain of this Iguanoid 
with those of the other species of Lacertilia with which I have 
dealt, I am unable to say anything about the cerebellar arteries, 
which were not visible in the specimen examined by me. The 
bifurcation of the basilar artery in front at rather an acute angle 
consisted of equally-sized vessels, and the carotids which joined 
these arteries behind the third pair of nerves were also equal. 
The arteries to the corpora bigemina disappear at once in the 
groove separating each corpus bigeminum from the hind brain. 
The other arteries of the brain seem to be as in other Lacertilia. 
$ Brain of Eumeces algeriensis. 
The arrangement of the arteries of the brain in this Skink, 
which, so far as I am aware, has not been described, shows 
certain differences from that of both Varanus and Jguana. 
These features are illustrated in the accompanying drawing 
(text-fig. 16, p. 62). The fusion of the vertebral arteries with 
the basilar marks, as 1s usual, the end of the medulla. From the 
basilar artery arise a number of branches of which the posterior 
cerebellar arteries are the most important; of these the left artery 
arises in advance of the right and it is shortly reinforced by 
another branch. The bifurcation of the basilar anteriorly begins 
further back than in both Varanws and Jqguana; and another 
difference from the conditions observable in these two genera is 
to be noted. In these Saurians the carotids join the circle of 
Willis behind the origin of the third pair of nerves; in Hwmeces 
these arteries join the circle of Willis well in front of the third 
nerves, and therefore also in front of the slender anterior 
cerebellar arteries, and of the artery supplying the corpus 
bigeminum on each side. This artery not only supplies the 
corpus bigeminum but also the cerebellum, and it sends a branch 
forward which runs parallel to the posterior cerebral artery, and 
like it is lost in the groove separating the fore brain from the 
mid brain. Between this artery and the middle cerebral or 
Sylvian is a slender twig hke that of Zguana which runs to the 
base of the optic nerves. The anterior cerebral, which gives off 
the ophthalmic artery, is considerably thicker than the middle 
cerebral artery. 
§ Brain of Gerrhosaurus. 
As is the case with Hwmeces, the basilar artery in Gerrhosaurus 
(see text-fig. 17, p. 62) divides rather further back than it does in 
either Jguana or Varanus. There is, moreover, a very distinct in- 
equality of calibre in the two arteries ; the right is in fact consider- 
ably larger than the left. This inequality does not, however, extend 
to the two carotids, which are equal in size. These join the circle 
of Willis only just in front of the point of origin of the anterior 
