66 ME. F. E. BEDDARD OX THE ENCEPHALIC [May 16, 



A noteworthy difference exists between the two specimens in 

 relation to the course of the large left carotid. In the one 

 brain this artery lies ontside of the dura mater for a large pai't 

 of its course, and gives oft' at least one branch to the brain which 

 perforated that membi-ane ; thus giving additional proof of the 

 fact that the carotid itself lies outside of the dura mater. In the 

 other brain I did not observe this state of aflairs. It follows 

 tliat the left carotid exhibits an aloofness from the brain which 

 is remarkable, and that the branches therefrom do not run on 

 the same plane with it. 



The arteries to the oj^tie lobes arise from the basilar artery after 

 its bifurcation, between this point and the entrance of the carotids, 

 and further back still there is a smallei' cerebellar artery. The 

 posterior cerebral artery is small and arises just in front of entrance 

 of the carotids. The next important artery is a cerebral, which 

 arises in front of the inflow of the cai-otids. This artery is the 

 middle cerebral or Sylvian of other animals, since it runs along the 

 rudimentary Sylvian fissui-e. The posterior cerebi-al is also partly 

 represented by soA^eral small branches of the artery to the optic 

 lobe. In front of the middle cerebral artery is a smaller anterior 

 cerebral artery. 



Anteriorly to this the circle of Willis is completed in the 

 following way : the large left carotid bifiu-cates to form the two 

 nearly equally stout ophthalmic arteries which of course accom- 

 pany the optic nerves. Just before this bifurcation the slender 

 right carotid eftects a junction with the common trunk. 

 Immediately in front of this a single trunk arises from the point 

 of bifurcation of the left carotid, which at once divides into two. 

 These vessels run closely side by side in the furrow which separates 

 the two hemispheres and rejoin at the extreme anterior end of the 

 brain, their course in fact recalling that of the callosal arteiies 

 in mammals. The arteries are by no means inconspicuous, as is 

 shown in the annexed figure (text-fig. 19, p. 65). 



I now draw, of course quite in a preliminary and tentative way, 

 a series of comparisons between the Ophidian and Lacertilian 

 brain artei'ies, enumerating the characters of the former in the 

 same order as already given (on p. 64) for the latter. 



§ Cerebral Arteries in the Ojjhidia. 



(1) The enti'ance of the vertebral arteiies into the anterior 

 S]3inal marks the end of the medulla oblongata. These arteries 

 seem to be stouter than in the LacertUia. 



(2) There is no markedly large pair of cerebellar arteries arising 

 from the basilar artery, but a number of more or less equisized 

 arteries supplying the cerebellum and adjacent region. 



(3) The two branches produced by the bifurcation of the basilar 

 are equisized. The anterior cerebellar arteries arise from the 

 bifurcated region. 



(4) The point of entrance of the carotids appears to be rather 



