1904.] OF THE BRAINS OF MAMMALS. 185 



symmetrically on either side a middle cerebellar a.rtery. Each 

 artery has two main branches. Here again the blood-supply to 

 the cerebellum from this ai'tery nrust be very small. In the 

 second and less pei-fectly injected brain a small branch on either 

 side arises behind the middle cerebellar, which may be one of the 

 bi-anches of the posterior cerebellar advanced rather forward. 

 Between the middle cerebellar and the bifui'cation of the basilar 

 artery to form the cii-cle of Willis are three or four transverse 

 arteries, of which one pair are particularly well marked in both 

 specimens. Immediately after the bifurcation of the basilar 

 artery arise the anterior cerebellar arteries, which are stout 

 arteries and of as great calibre as any given off from the circle of 

 Willis. They constitute the main if not the only blood-supply of 

 the cerebellum. The third nerve sepai-ates this artery from the 

 posterior choroidal, which is of less calibre. Between this artery 

 and the posterior cerebral arises an artery of about the same di- 

 mensions which is an adjunct of the latter, and on the light side 

 of one specimen arises in common with it from the circle of Willis. 

 The j)osterior cerebral ai-tery is of the same calibre as the other 

 cerebrals and the antei-ior cerebellar. The circle of Willis is long 

 and narrow, relatively speaking. About halfway between the 

 posterior and middle cerebral arteries, exactly on a level with the 

 pituitary body, the very slender ophthalmic arteries join the circle. 

 The dimensions of these arteries are not greater than those of some 

 of the more inconspicuous biunches of the basilar axteiy ; but as 

 both specimens were identical in this particular, I take it that the 

 state of affairs is normal. Just before the origin of the middle 

 cerebral arteries arises a small artery on either side supplying the 

 temporal lobes of the cerebrum. As this vessel occurred in both 

 brains, I take it to be of some little importance. The middle 

 cerebral artery suj)plies, as will be seen from the diawing (text- 

 fig. 16, p. 184), the greater part of the cerebral hemispheres. 

 The anterior cerebral arteries are unconnected by any anterior 

 communicating artery, but apparently pass into one in the region 

 of the corpus callosum, thus completing the circle. 



In the allied Lagostomus trichodactylus the characters of the 

 brain ai-teries appear to me to be the same in all essentials. The 

 ophthalmics and the anterior spinal artery are minute. This 

 brain, however, enables me to ascertain one point which is very 

 possibly the same in Chinchilla, but which I was not able to 

 elucidate in that rodent. In LagostoimijS the anterior cerebral 

 artery of the left side divides at once into two large and equisized 

 branches, of which the outer supplies the under surface of the 

 anterior lobe of the brain, whilst the other f)lunges into the inter- 

 hemispheral sulcus, and is the main anterior cerebral trunk. It 

 soon divides above the corpus callosum into two branches. In 

 Chinchilla it is also apparently the left branch only which supplies 

 the (in this case single and median) anterior cerebral artery ; but 

 a break in the right branch supplying the under sui-face of the 

 hemispheres does not allow me to speak with absolute certainty. 



