1905,] ARTERIES OF THE BRAIN IN BIRDS. 105 



which the anterior bends inwards and gives off branches which 

 anastomose with those of the anterior cerebral. The latter artery- 

 is about equal in size to either the middle or the posterior cerebral, 

 and arises along the circle of Willis some way in front of the 

 middle cerebral. The two anterior cerebrals anastomose anteriorly 

 in the middle ventral line of the brain. 



Dromceus 7iovce-hollandice. — A beautifully injected brain of this 

 species shows some differences fi-om that of the Ostrich. 



The space enclosed by the anterior bifurcation of the spinal 

 artery and the i-eunion of the vessels to form the basilar artery 

 is somewhat more extensive than in Struthio. There is an 

 asymmetry in the relations of the cerebellar arteries to the 

 trunk of which they are branches ; but the asymmetry is dif- 

 ferent. The spinal artery arises from or joins the right cerebellar, 

 and both of the cerebellar arteries lie in front of the sixth pair of 

 nerves, instead of one in front and one behind as in Struthio. The 

 bifurcation of the basilar artery anterioi-ly is rather peculiar in 

 the specimen before me. There is the usual asymmetry, but it is 

 unusual in its character. Just behind the optic chiasma the 

 basilar artery bends to the right side of the brain and becomes 

 continuous with the carotid in the usual way. About halfway 

 between the point where the basilar artery becomes deflected to 

 the right and its bifurcation posteriorly to form the cerebellar 

 arteries, an artery of one-half of the diameter of the basilar arises 

 from it on the left, and after giving off branches to the medulla 

 runs forward and becomes connected with the left carotid. 

 Anteriorly the - carotids give off the usual arteries ; but their 

 main stem is the middle cerebral artery, which passes along the 

 Sylvian fissui'e. The ophthalmic artery arises at the root of this, 

 and immediately afterwards, apparently almost by a common stem 

 with the ophthalmic, the anterior cerebral. This artery divides on 

 each side into two branches, fairly equisized, of which the inner 

 supplies the olfactory bulbs, which are here large. It is as well 

 developed as in Goura (desci-ibed below), and much more con- 

 spicuous than the minute corresponding artery of Struthio. The 

 outer bi'anch of the anterior cerebral again divides into two 

 equisized branches, as is the case with Stru,thio. 



Ara hyacinthina (text-fig. 16, p. 106). — The anterior spinal artery 

 is single throughoiit and slender, but shows no such great dispro- 

 portion in calibre to the basilar artery such as is apparent, for 

 example, in the Penguin, Spheniscus demersus, desciibed below. 

 It is, however, rather more slender than the basilar artery. The 

 two aiteries do not pass directly into each other ; for the anterior 

 spinal opens into the left cerebellar artery, quite close, however, 

 to its point of origin from the basilar artery. The cerebellar 

 arteries, with the slight exception just mentioned, are symmetrical 

 and arise behind the origin of the sixth pair of nerves. 



It is important to note that in this bird the basilar aitery is 



