188 MR. F. E. BEDDARD ON THE ARTERIES [Feb. 2, 



the conjoined vertebrals I was unable to see*. It is evidently 

 therefore longer than in some other forms. Another peculiarity 

 is that all three cerebellar arteries — not merely the two posterior — 

 arise fi-om the undivided basilar artery. A still more remarkable 

 peculiarity, again, is shown in a complete absence on the right 

 side of any connection between the basilar artery and the posterior 

 cerebral. The circle of Willis is thus incomplete posteriorly. On 

 the other side of the body the basilar artery, after passing straight 

 forwards under the pituitary body, bends sideways and is con- 

 nected with the left postei-ior cerebral artery. The anterior com- 

 municating artery is, however, present on both sides, as is shown 

 in the drawing (text-fig. 18, p. 187), and connects the anterior 

 and middle cerebral arteries. Quite posteriorly, in fact behind 

 the third nerve, the communicating arteries end in the carotid. 

 These arteries are large, and it is interesting to note that their 

 position, at the posterior end of the circle of Willis, is precisely 

 the same as it is in the Horse ; and that so far, therefore, Hyrax is 

 nearer to the Perissodactyle t than to the Artiodactyle section of 

 the Ungulates, in which latter the carotid does not, as a rule, 

 reach the circle of Willis at all. 



The ophthalmic arteries are of less calibre than the posterior 

 communicating arteries, which they join well behind the circle of 

 Willis. They are, however, by no means rudimentary in character. 

 Before giving off the middle cerebral, the anterior communicating 

 artery of each side gives off a well -developed bi'anch to the 

 hemispheres, upon the presence of which I have commented in 

 Chinchilla and other mammals. The anterior communicating 

 artery is formed by a longish commissure uniting the two very 

 strong olfactory arteries, from the middle of which commissure 

 arises the slender and at first single anterior cei'ebral artery. 



Tamandua tetradactyla. — Hyrtl and Tandler J have dealt with 

 some of the cerebral arteiies of this Edentate. But my own 

 results derived from the study of a well-injected brain supple- 

 ments those of the two anatomists mentioned. 



The condition of the basilar artery appears to me to explain the 

 apparently abnormal length of the same in Hyrax. At first 

 sight there appears to be an exact correspondence. A closer 

 examination, however, shows that, at a distance of 17 mm. behind 

 the circle of Willis, the basilar artery divides into two branches, 

 which almost immediately i-eunite, enclosing a brief rhomboidal 

 space, as is clearly shown in the drawing (text-fig. 19, p. 189). 

 What has happened is evidently an exaggeration of the median 

 anterior spinal artery, and a reduction of the interval lying 

 between the anterior bifurcation of this artery and the posteiior 

 bifurcation of the basilar artery. Hyrax, as it appears to me, is 



* I may observe that the brains which are described here consist of the brain 

 itself and of the cord down to the atlas. Before the brains are extracted the cord is 

 cut as near to the atlas as possible. 



t Chauveau, ' Traite d'Anatomie Comparee des Animaux Domestiques,' 2nd ed. bj"- 

 Arloing (Paris, 1871), p. 618, fig. 241. 



X Who summarises previous observations. 



