ZOOLOGICAL AND BOTANICAL ASSOCIATION. 225 



overlooked, opens just within the posterior nares; it is narrow, but 

 wider in the allied animal. A vidian nerve and other twigs, a tensor 

 tympani muscle, &c, may also be found in the tympanum. The coch- 

 lea makes only a single turn in both ; the semicircular horns have been 

 mentioned before; in the Ornithorhynchus, one surrounds the opening 

 of the side cavity of the skull, this giving origin to a second, which 

 descends to the vestibule, just outside the condyle ; whilst the third lies 

 horizontally in the floor of the said cavity. The eighth and ninth 

 nerves in the Ornithorhynchus leave the skull by a large opening be- 

 fore the condyles, principally closed by membrane ; in the Echidna by 

 small openings in the temporal bone. 



Whilst the Ornithorhynchus may be considered a four-legged and 

 wingless duck, the Echidua is, as is well known, an ant-eater, having 

 a very long, extensile, and viscid tongue, and its mouth situated at the 

 end of a tubular and callous muzzle, which of course must want the 

 extraordinary nerves of the former animal. My two specimens of 

 Echidna had evidently been amongst the ants, and the friend who for- 

 warded them said that the strength of the animals, when dug up, was 

 enormous, that they burrow in banks, and can roll themselves up into 

 a ball. How beautifully the Ornithorhynchus or Platypus, as the colo- 

 nists call it, is adapted to obtain its food, consisting of insects and mol- 

 luscs found at the bottom of rivers in the mud or sand, must strike any 

 observer. 



In three or four species of Hypsiprimnus and Phalangista, Tasma- 

 nian Marsupials, the Potaroos and Opossums of the colonists, the brain 

 was principally remarkable for the peculiarity mentioned above, the 

 absence of a corpus callosum, the fornix somewhat takiDg its place, and 

 having in front four processes, two going forwards above the anterior 

 commissure, and two downwards behind it. The cerebrum in all was 

 perfectly smooth, the cerebellum laminated. There were moderate-sized 

 olfactory bulbs in front, the cerebellum having the small side lobules, 

 the corpora quadrigemina well marked, equal, and a little exposed ; the 

 hippocampus large. In fact, with the exception of the absence of the 

 corpus callosum, leaving the third ventricle exposed between the hemi- 

 spheres, or only covered by the velum and the posterior part of the fornix, 

 these brains may well be compared with that of a hare or a rabbit. 



A few words on the brains of those curious little animals, the moles, 

 two or three species of which I have examined, including the curious 



