64 MR. F. E. BEDDARD ON THE ENCEPHALIC [May 16, 



chai'acters 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 afe the only conspicuous 

 arteries arising fi'om the basilar ; they aidse 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 antei-ior bifurcation of the basilar is at a more or less 

 acute angle according to its position ; the slender anterior 

 cerebellar ai'tei-ies are invai-iably given off from the bifurcated 

 basilar behind the j)oint of origin of the third nerves ; the two 

 bi'anches of the basilar produced by the bifurcation may be 

 inequisized . 



(4) The point of entrance of the carotids is not invaria,bly 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 enti-ance of the carotids. 



(6) In front of this artery is one which runs towai-ds the optic 

 chiasma. 



(7) There are three cerebral or hemisiDheral arteries : the 

 posterior reaches each hemisphere just at its junction with tlie 

 corpus bigeminiun ; the middle one is Sylvian in position ; the 

 anterior cerebral gives off the oj)hthalmic ; 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. 



§ Brain of Python molurus f. 



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 othei- Savu'opsida is 

 the marked asymmetry in the aiterial system (text-fig. 19, p. 65), 

 which agrees of course with the vasculai- 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 I'uns 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. 

 t Rathke describes but does not figure brain-ai'teries of Ophidia i)i Denkschr 

 Akad. Wiss. Wien, xi. 1855. 



