64 MR. F. E. BEDDARD ON THE ENCEPHALIC [May 16, 
characters of the encephalic arterial system in the Lacertilia for 
purposes of comparison with those of other Vertebrates *. 
{1) The entrance of the vertebral arteries into the anterior 
spinal marks the end of the medulla oblongata. 
(2) The posterior cerebellar arteries are the only conspicuous 
arteries arising from the basilar; they arise at about the middle 
of the medulla oblongata and behind the 6th pair of cranial 
nerves; they are occasionally asymmetrical with each other. 
(3) The anterior bifurcation of the basilar is at a more or less 
acute angle according to its position; the slender anterior 
cerebellar arteries are invariably given off from the bifurcated 
basilar behind the point of origin of the third nerves; the two 
branches of the basilar produced by the bifurcation may be 
imequisized. 
(4) The point of entrance of the carotids is not invariably the 
same; it is sometimes in front of and sometimes behind the third 
pair of nerves. 
(5) The artery on each side to the corpus bigeminum sends 
branches to the cerebellum and to the cerebral hemispheres. It 
arises in front of the entrance of the carotids. 
(6) In front of this artery is one which runs towards the optic 
chiasma. 
(7) There are three cerebral or hemispheral arteries: the 
posterior reaches each hemisphere just at its junction with the 
corpus bigeminum ; the middle one is Sylvian in position; the 
anterior cerebral gives off the ophthalmic; there is no distinct 
completion of the circle of Willis anteriorly. 
(8) There is no strongly marked asymmetry in the cerebral 
arterial system of the Lacertilia. 
S$ Brain of Python molurus 7. 
I have been able to study two injected brains of this serpent, of 
which one is more completely injected than the other. The most 
obvious and plain difference from the brains of other Sauropsida is 
the marked asymmetry in the arterial system (text-fig. 19, p. 65), 
which agrees of course with the vascular asymmetry shown else- 
where among the Ophidia. This asymmetry, however, only concerns 
the carotids. The other arteries of the brain, so far as I have been 
able to study them, do not show anything of the kind, but indeed 
a perfect regularity quite comparable to that shown in other 
Sauropsida. Of the two carotids the left is very much the larger. 
The basilar artery is single where it runs along the ventral surface 
of the cord and brain, until of course it bifurcates anteriorly at 
the commencement of the circle of Willis. The entrance of the 
vertebral arteries marks the end of the medulla. These arteries, 
which lie exactly opposite to each other, are very much stouter 
than the basilar, which they combine with the anterior spinal to 
* See below, pp. 66, 67, and 69, for comparison with Ophidia and Testudinata. 
+ Rathke describes but does not figure brain-arteries of Ophidia in Denkschr. 
Akad. Wiss. Wien, xi. 1855. 
