106 



ANATOMY OF VERTEBRATES. 



sylvian convolution, e, e' 9 folded on 5, is divided behind by the 

 fissure, 9, from the post-sylvian fold, f. The contracted anterior 

 part of the hemisphere is marked off by a feeble coronal fissure, 

 12, and is partially divided into a superfrontal fold, rc x , and a 

 subfrontal fold, n'. In the broad hind part of the hemisphere 

 are the medial, Z, and lateral, m, tracts. 



On separating the hemispheres of the brain of the Wombat, 

 not only the bigeminal bodies, B, fig. 75, and pineal gland, ib. 

 u, but the thalami, ib. t, t, are brought into view, and instead 

 of a broad corpus callosum, we perceive, situated deeply, a small 

 commissural medullary band, ib. m, passing in an arched form 

 over the anterior part of the thalami, and extending beneath 

 the ( labia hippocampi,' the supraventricular part of the hemi- 

 spheres, q 9 being thus, as in 

 the bird and monotreme, dis- 

 connected with each other. 

 On gently raising the labia 1 

 from above the commissure 

 and pressing them outward 

 with the handle of a scalpel, 

 the instrument passes into the 

 fissure upon which the hippo- 

 campus, ib. n, is folded. The 

 mesial wall of the hemisphere 

 is continued from the upper 

 labium of the hippocampus, 

 and is composed of a thin 

 lamina of medullary substance 

 analogous to a detached layer 

 of the septum lucidum. In the 

 Kangaroo the mesial parietes 

 of the lateral ventricles are 

 thicker. In both Marsupials they receive the thin layer of fibres, 

 fig. 75, o, passing from the commissure, m, over the upper lip of 

 the hippocampal fold, to radiate vertically upon the anterior half 

 of the inner wall of the ventricle. These fibres are figured in 

 lxx'. i)l. vi. fig. 4, o' (Wombat), and fig. 6, o' (Kangaroo), and 

 are described as the 6 anterior fibres of the taenia hippocampi 

 continued into the anterior lobes of the hemispheres.' 2 



1 These are not to be confounded with the ' labia cerebri ' of anthropotomy. 



2 The author of xliii". figures, in pi. xxxvi. fig. 4, a more extensive series of trans- 

 verse fibres which he describes, p. 644, as being lost beneath the ' labia cerebri,' as 

 the margin of the ' callosal fold ' is called by some authors. The surface of the diva- 



Phascolomys fusca. 



