166 MR. F. E, BEDDARD ON THE [ Feb. 16,. 
the right side of the circle of Willis. It is clear, however, that 
this specimen was so far abnormal; for in nine others (the only 
ones in which the arteries were visible) both divisions of the 
basilar artery were plainly present, thus completing the symmetry 
of the circle of Willis. 
I find that asa general rule the basilar artery is undivided upon 
the medulla, as I have figured it in Hyrax *. But in two out of 
the nine specimens the artery formed a loop, such as I have 
figured in Zamandua, but longer. Such a bifurcation and re- 
junction of the basilar artery is very common among Ungulates. 
In each case the vertebral artery on either side joins the anterior 
rhinal artery behind the loop. These arteries mark the end of the 
medulla oblongata. Imay remark that a misinterpretation of the 
woodcut illustrating the arteries of the base of the bra in 
Equus in Messrs. Chauveau and Arloing’s treatise, led me _ to- 
compare Hyrax especially with Hquus in the posteriorly situated 
communication of the carotid with the circle of Willis. They are 
as a matter of fact anteriorly placed in the Horse as in the 
Rhinoceros 7, and posteriorly placed in Hyrax. In five examples 
of Hyrax | found that the carotid became continuous with the 
circle of Willis just opposite to the origin of the posterior cerebral 
artery. The other specimen examined by me did not show the 
relations of the artery with great clearness. I mention this matter 
particularly since it is not dealt with in my original figure of the 
arterial system of the brain. I find that the arteries at the base 
of the brain in Hyrax differ in another particular, unless indeed I 
have made an error in my former description. For I find that in 
several brains the anterior cerebellar artery arises on each side 
from the bifureate basilar artery, and not from the latter posteriorly 
to its bifurcation. In spite, however, of these few additions to 
the description of the arrangement of the arteries forming the 
circle of Willis, it remains clear that Hyrax comes nearer in 
respect of these structural peculiarities to the Perissodactyle than 
to the Artiodactyle section of the Ungulates, a position upon 
which I ventured to insist in the paper already quoted. 
Cecum and gut of Hyrax dorsalis.—Of this species of Hyrax I 
have recently dissected two examples which permit me to compare 
certain organs with the corresponding organs in Hyrax capensis 
and Hyrax syriacus. In the general subdivisions of the cecum of 
H. dorsalis 1 find no cuatrences from those of H. capensis. When 
the cecum is viewed on the opposite side to that on which the 
ileum enters it, two muscular bands as in H. capensis are seen to 
traverse the cecum, forming by their contraction two parallel 
furrows upon the surface of the cecum; these ultimately join to 
form a single muscular band and furrow. The junction is, how- 
ever, considerably further forward in Hyrax dorsalis, at a point 
in fact corresponding to the end of the first two-thirds of the 
entire length of the cecum. Furthermore, while in H. capensis 
* Loc. cit. p. 189, text-fig. 19 b. 
+ Beddard & Treves, Prans. Zool. Soe. vol. xii. pl. xxxvil. 
