1905. | ARTERIAL SYSTEM IN SAUROPSIDA. 67 
fay forward as compared with the Lacertilia; but this appearance 
is at least partly due to the great length of the bifurcate region 
of the basilar artery in Python as compared with that of any 
Lacertilian. 
(5) The artery to the corpus bigeminum on each side arises 
behind the entrance of the carotid instead of in front as in 
Lacertilia. It gives off branches to the cerebrum and also to the 
cerebellum. 
(6) In front of this artery and also in front of the carotid is an 
artery which runs towards the optic chiasma. 
(7) There is a very marked completion of the circle of Willis 
anteriorly. 
(8) There is a strongly marked asymmetry in the arterial 
system of the brain due to the greater size of the left carotid. 
§ Brain of Testudo vicina. 
The most salient characteristic of the arterial system in this 
Reptile is the double basilar artery (text-fig. 20, p.68). The artery 
is double for the whole of its course beneath the medulla oblongata. 
The anterior spinal artery in fact divides into two well behind 
the medulla. The right-hand one of the two branches is not 
larger than the left; the two arteries do not run close side by 
side, but are separated by a considerable distance. They are 
joined each of them by the carotid in front of the origin of the 
third nerve. Behind the origin of the third nerve a large number 
of arteries arise from the basilar on each side; there are certainly 
eight or nine of them on each side, and they supply the cerebellum, 
the medulla, and the cranial nerves of this region of the brain. 
The fifth artery (on the right side at any rate), which arises from 
the basilar behind the third nerve, is par excellence the cerebellar 
artery ; it fuses with its fellow of the opposite side at the end 
of the cerebellum. In front of the third nerve arise two arteries 
rather close together, of which the anterior has several branches 
and is the larger artery: it partly supplies the cerebral hemi- 
spheres and corresponds, as I imagine, to that artery in the 
Lacertilia which supplies the corpus bigeminum on each side. 
Asinthe Lacertilia, there are two cerebral arteries on each side. 
The first and largest of these (text-fig. 21, p. 68) may be termed the 
Sylvian, as it runs along the lateral groove upon the hemisphere 
which has been compared to the Sylvian fissure of mammals The 
branches of this artery are not altogether symmetrical on tne two 
sides of the body; it is possible, however, to distinguish the main 
trunk which runs towards the top of the brain, where it divides 
into a forwardly running anda backwardly running branch, several 
branches from the main stem which pass backwards over the 
temporal region of the hemisphere, and a strong branch running 
forwards to the olfactory lobe. Moreover, there is plain on one 
side a branch arising immediately after the origin of the Sylvian 
artery, which plunges at once beneath the hemisphere. A second 
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