190o.] ARTERIES OF THE lUlAIX IX BIRDS. 113 



branch on the right side to form or join the circle of Willis ; on the 

 opposite side is a very slender equivalent artery. The ophthalmic 

 (text-fig. 19, Opth.^ p. 112) arises from the circle of Willis in a way 

 which is found in some other birds, but not in all. Each artery 

 arises from the circle of Willis before the latter gives ofi' the middle 

 cerebral artery. The anterior cerebral is therefore quite indepen- 

 dent of the ophthalmic artery, instead of being a branch of it as it 

 is, for example, in the Ostrich. Tantalus agrees more neatly with 

 Pelecanus than with some other birds in the disposition of these 

 arteries. The middle cerebral artery gives ofii" as usual a large 

 series of branches, but there is not an especially conspicuous one 

 curving round towards the middle ventral line of the brain as in 

 so many birds. This region of the brain is, in fact, supplied by 

 the anterior cerebral arteiy (text-fig. 19, A.cer^i. Tliis artery has 

 two chief branches : the one runs forward towards the olfactory 

 lobes ; the other runs along the groove lying in front of the optic 

 chiasma and nearly meets its fellow of the opposite side. The 

 position occupied by this artery is, in fact, exactly that which is 

 often occupied by the ophthalmic arteries in other birds. It is 

 remarkable that in the Ostrich (text-fig. 15, p. 103) the ophthalmic 

 does occupy this position, and that, furtlier, an artery arises from 

 the circle of Willis exactly in the position of the ophthalmic artery 

 in Tantalus, and runs to tlie optic nerve on either side. This 

 artery lies above the ophthalmic, and is shown on the right side 

 only in the figure (text fig. 15, p. 103). 



Anthropoides paradisea. — In this Crane I have been able to 

 study the brain arteries in considerable detail ; the injection had 

 been very successful. The anterior spinal artery shows the veiy 

 usual bifurcation and reunion before uniting with the cerebellar 

 arteries to form the basilar. The reunion takes place some little 

 way behind the entrance of the anterior spinal artery into the 

 right cerebellar artery. This union, it will be observed, is, as in 

 so many other bii'ds, the cause of an asymmetry in this region of 

 the vascular system of the brain. The basilar artery gives off in 

 its course two pairs of quite symmetrically di~ijiosed arteries to 

 the medulla. The basilar artery itself ordy supplies the right side 

 of the circle of Willis. 



Cariama cristaia. — The anterior spinal artery in Cariama is, as 

 is usual among birds, unsymmetrical with regard to the basilar 

 artery ; it is not in the same straight line with it, but joins the right 

 cerebellar. Towards the end of the medulla the anterior sj)inal 

 is double, the right-hand half being, however, the more important. 

 The calibre of the anterior spinal is less than that of the basilar 

 artery, but the difference is not so great as in some birds, for 

 example the Penguin. The basilar arteiy does not bifurcate 

 anteriorly, but joins the right side of the cu'cle of Willis only ; 

 just before joining it emits the artery to the right optic lobe. 

 The cerebellar arteries — at any rate that of the left side — arise in 



Pkoc. Zool. Soc— 1905, Yol. I. No. YJII. 8 



