TRANSACTIONS OF THE SECTIONS. 123 
On the Oyster. By T. C. Eyton, F.L.S. 
At the Cheltenham miceting the author exhibited the young oystertaken from the beard 
of the parent. He now traced the young oyster from the embryo state in the ovary 
to its perfection at five years old; and exhibited a series of drawings on the history 
of the oyster, the mode of preserving the beds and increasing their productiveness. 
On the Anatomy of the Brain in some small Quadrupeds. 
By Rosert Garner, #.L.S. 
The comparative anatomy of the brain, little studied in Great Britain (Professor 
Owen having been one of the few labourers in the field), has on the continent met 
with more attention, witness the accurate researches of Tiedemann, Desmoulins, and 
Leuret. As the importance of the subject in regard to zoology and physiology 
cannot be doubted, the writer offers the description of the brain in a few small but 
interesting quadrupeds dissected by himself. 
The two genera constituting the great family of quadrupeds, called Monotremata, 
similar in some respects, as far as the brain is concerned, are in others remarkably 
different. The Echidna Histrix has well-developed convolutions to its brain, that 
of the Ornithorhynchus paradoxus is only marked by the rather deep grooves of its 
vessels ; it has, too, a bony lamina between the hemispheres, which is wanting in the 
other. The former has the olfactory bulbs very large, the latter much less. The 
Echidna has not the little side lobules of the cerebellum, which in the Ornitho- 
rhynchus are remarkable, occupying cavities in the temporal bone, and encircled by 
the three semicircular auditory canals ; in the Echidna these last also exist, but deep 
in the solid bone. The Ornithorhynchus has the two posterior prominences of the 
corpora quadrigemina very little developed, less than in any other quadruped, if we 
are not mistaken, making therefore a gradation to their disposition in birds. Both 
have the peculiarity (general, it would appear, in the Marsupialia and Monotremata) 
of the absence of the corpus callosum. The two principal commissures are the an- 
terior and the fornix, both well-developed, the latter being continuous behind with 
the hippocampus major; itself very large in such animals as have large olfactory 
bulbs and tracts, with which it is connected. The remaining parts do not much 
differ from other quadrupeds. 
With respeet to the organs of sense, and the cerebral nerves supplying them, we 
may commence (having already noticed that the olfactory organs are enormously 
developed in the Echidna) by observing that the eye of the aquatic species, the Or- 
nithorhynchus, has a supplementary valvular lid, the lens also being more convex 
than in the Echidna. There is a lacrymal apparatus and duct in the usual place. 
The cerebral nerves generally are upon the normal plan, but the duck-billed creature 
has the fifth nerve very greatly developed to supply its curious mandible, which must 
possess extraordinary sensibility, though of a subdued kind, from its leathery cover- 
ing; similar to that of a hand with fine touch enveloped in a closely-fitting glove. 
The large nasal branch of the first or ophthalmic division of this fifth nerve, running 
in a peculiar canal, and the second division, of course, supply the upper mandible, 
and the third the lower. Six fascie of nerves, generally very large, are dis- 
tributed to the former, and four to the latter, on each side. The author is not 
sure whether mention is made in authors of the little saccular organs with 
papillz, situated on the front of the palate, immediately under the nostrils, the latter 
situated, of course, above, on the upper surface of the bill. Home does mention four 
rudimentary anterior teeth in addition to those commonly enumerated: The origin 
of the gieat fifth nerve is evidently below the pons from the medulla oblongata. 
The external ear-canal is long and sinuous in the Ornithorhynchus, with a wider 
opening and more regularly curved in the Echidna. The drum of the ear looks 
downwards in this last, a little forwards and outwards in the first, and here too it is 
smaller and longer. In both, the membrane is stretched on a separate rim of bone 
like a tambourin. Home and Blainville give only two bones, but there is a loose 
quadrate bone attached to the malleus, and on which the trumpet-shaped stapes 
rests; this must be the incus. The malleus is large and connected with the bony 
circle, and also, as usual, with the membrane. In the Echidna the narrow Eusta- 
