174 PHYSIOLOGICAL SERIES. 



which the whole of the neopallial fibres of the ventral 

 commissure behave in the Monotremata (fig. 42), the Poly- 

 protodont Marsupialia, and the Eutheria. But in ALL the 

 Diprotodont Marsupials the dorsal half of the vent ml 

 commissure bends upwards in the corpus striatum, as it does 

 in this section, and ultimately reaches the neopallium by the 

 >ame route as that pursued by the internal capsule. This 

 dorsal bundle I have called the "fasciculus aberrans" It 

 was first represented in a figure by Flower (Phil. Train. 

 1865), and first described by Symington (Journ. of Anat. A: 

 Phys. 1892) in Macropus. 1 have recently examined the 

 brain in every genus of the Marsupialia (excepting Caeno- 

 lestes), and found this *' aberrant bundle" to be invariably 

 present in the Diprotodontia, but never in the Polypro- 

 todontia, nor in other mammals. [This fact is here recorded 

 for the first time.] 



The third section passes through the hemispheres a short 

 distance behind the commissures, and the " splenium " 

 of the hippocampal commissure is still seen in the depth-; of 

 the slice above the slit-like third ventricle, which separate- 

 the optic thalami. This section passes through the optic 

 chiasma. 



The fourth section has been cut still further back. It 

 exhibits the fimbria on the hippooampol formation, and it 

 U easy to understand by comparison with the third section 

 how the fibres of the fimbria reach the dorsal commissure. 



O.C, L323 U 



Symington, Journ. of Anat. & Phys., vol. xxvii. 1892, 

 p. (59. 



D. 210. The left cerebral hemisphere of a Yellow-footed Hock- 

 Wallaby ( I'ftrogale xanthopm), from which the lateral 

 will of the ventricle hat been removed in order to expose 



the hippocampus (fig. f>f>). 



The disposition of the hippoctfrnpofl is the most character- 

 istic fi'.-itnre of the brain in Marsupials, in all of which. 

 both Poly- and Diprotodont. it presents a constant arrange- 

 ment such as this specimen exhibits. Instead of being 

 n-tricted to the descending limb and posterior part of the. 

 Ixxly of the lateral ventricle, as is the case in most 



