1909.] STRUCTURE OF THE LESSER ANTEATER. 685 



injected. I am able to compare this brain with that previovisly 

 described. It is interesting to notice that there are no important 

 diflerences between the two brains in respect of their arterial 

 system, which tends to inspire confidence in the fixity of this 

 character. The rhcmboidal space at the end of the medulla, 

 formed by the division and subsequent reuniting of the basilar 

 artery, was identical in the two specimens. In his figure of the 

 cerebral arteries of this animal, Hyrtl * has not repi-esented the 

 space referred to ; so that there may be some variation. He has, 

 however, noted — and I find that the second specimen examined 

 by myself agrees with that figured by Hyrtl and with that figured 

 by myself t — that the anterior communicating artery gives off a 

 strong forwardly-running branch, which immediately loses itself 

 between the hemispheres as the callosal artery. I shall refer to 

 some further details in considering the corresponding arteries in 

 Myrmecopliaga jidiata, of which I possess a well-injected brain. 

 The cerebral arteries of this species have been described and 

 figured by Pouchet J . This paper is not ref eri-ed to by Tandler § or 

 ]\j;iie (-\e Vrieseli, who have mentioned a great many other important 

 papers upon the cerebral arterial system of the Mammalia. I find 

 myself in general agreement with Pouchet's figure, though my 

 specimen shows some differences from the individual studied by the 

 French anatomist. I find that the circle of Willis is distinctly 

 hourglass-shaped — more mai-kedly so than in Tamandua. The 

 carotids enter at the " waist" of the hourglass, as among Artio- 

 dactyles, where the circle of Willis has, as is well known, the same 

 hourglass-shape. Anteriorly the arch of Willis is completed by 

 the anterior communicating artery. This runs pei-fectly straight 

 across the intervening space, and gives off" no strong callosal 

 artery like that of Tamandida. There are only some quite small 

 branches. The Sylvian arteries (or middle cerebrals) arise from 

 the circle of Willis asymmetrically. The right-hand artery arises 

 exactly opposite to the anterior communicating artery ; the left- 

 hand artery (which arises by two roots, which immediately join) 

 is behind the corresponding point on the left side. Between 

 these arteries and the posterior cerebrals are two smaller arteries, 

 on each side, of which the first arises just behind the exit of the 

 carotids. The latter artery (on the left side only ; there was not 

 enough of it preserved on the right to permit of a statement) 

 gives off" immediately before it reaches the circle of Willis an artery 

 running anteriorly, which I take to be the ophthalmic artery. 

 The posterior cerebral arteries are rather asymmetrical, as will be 

 seen from an inspection of text-figure 218 (p. 686). On the right 

 side there is only one large artery, which, however, very shortly 

 divides into two branches. On the left side three fair-sized arteries, 



* Beitrage z. vergleichenden Angiologie, v. ; Denkschr. k.-k. Akad. Wien, vi. 1854 

 p. 21, pi. iv. 



t P. Z. S. torn. cit. p. 189, text-fig. 19. 



X ' Mem. sur le Grand Fourmilier,' Paris, 1874, pi. xiv. fig. 1. 



§ Denkschr. k.-k. Akad. Wien, Ixvii. 1898. 



II Arch, de Biol. xxi. 1904, p. 449. 



