1891.] BRAIN OF THE MALE THYLACINE. 143 



coupled with the divergence of the two hemispheres posteriorly, 

 leaves the corpora quadrigemina partially exposed. The degree to 

 which the corpora quadrigemina are exposed is about the same as in 

 the Kangaroo, but considerably less than in the Wallaby or Opossum, 

 or for the matter of that in the Eodent Bolichotis, the brain of which 

 I propose to describe later. 



The cerebral hemispheres are not greatly convoluted. Judging 

 from Owen's figures of the Opossum and i\\& Dasyurus ursinus, there 

 is a progressive complication of the folds in passing from the 

 smaller to the larger forms, such as is often seen among mammals ; 

 the Thylacine, which is the largest animal, has the greatest develop- 

 ment of furrows of the three. Nevertheless the brain of this Mar- 

 supial is much smoother than that of a Kangaroo of about the same 

 size. Sir Richard Owen's figure of the Dasyure's brain ' is a little 

 indistinct; I am not therefore able to compare it with the Thylacine 

 very accurately. As compared with the Kangaroo", the sulci are 

 less numerous and often shallower. 



In the Kangaroo's brain the Sylvian fissure is deep and the con- 

 volutions are arranged in a series of arches round and above this 

 fissure, as in the Carnivora ; the " arched " arrangement is perhaps 

 not so plain as in the Carnivora, and there are only two arches. In 

 the Thylacine such an arrangement of the gyri could not be made 

 out, the principal furrows passing obliquely so as to divide the brain 

 into three unequal segments. The furrow separating the hemispheres 

 proper from the olfactory portion (the hippocampal gyrus) is well 

 marked, and as usual is bent upwards at about the middle of its 

 course, but the angle formed is not so acute as in Macropus. From 

 the highest point of this bend arises the Sylvian fissure {S, fig. 2, 

 p. 141), which passes nearly vertically upwards and is about half an 

 inch in length. On one side of the brain the Sylvian fissure could 

 be followed as a very shallow groove into the posterior of the two 

 principal sulci. 



On a dorsal view the hemispheres are seen to be divided into 

 three unequally sized areas by two furrows running obliquely and 

 approximately parallel to each other. The posterior fissure reaches 

 the middle line of the brain 29 mm. in front of its posterior 

 boundary, i.e. 19 mm. behind anterior boundary of hemispheres. 

 On the left side of the brain this fissure runs parallel with the rhinal 

 fissure; the commencement only is shown in Gervais's figure: near 

 to its posterior termination it gives off a short descending fissure 

 which does not reach the rhinal fissure, but stops short about a 



^ Loc. cit. pi. V. fig. 5. 



2 I follow Owen's figure (Phil. Traus. 1837, pi. v. fig. 4, and pi. vi. fig. 1), 

 which, except for .some slight dilFereuces, probably iudividual, agrees with a 

 brain in my possession. Gervais's figure of the brain of a " Kangurou geant " 

 {loc. cit. pi. 13. fig. 1), which I take to be the same species, is that of a larger 

 individual (?) and is more convoluted, and the convolutions are a little different ; 

 but the cast which he figures is like the brain before me. Sir W. Turner's figure 

 (" The Convolution of the Brain ; A Study in Comparative Anatomy," Journ. 

 Anat. Pbys., Oct. 1890, p. 118. fig. 11) of Macropus major is nearly identical with 

 the brain I have examined. 



