384 
transparent; the membranous falx is less deep 
than the osseous one of the Ornithorhynchus. 
I found no bony plate between the hemi- 
spheres in the Echidna. The arachnoid is 
transparent, but relatively strong. The cere- 
bellum is traversed by several narrow trans- 
verse anfractuosities, disposed as in fig. 182. 
The vermiform or alien lobe, as in the 
Ornithorhynchus, is larger in proportion to 
the lateral lobes than in the Marsupialia, and 
the limits between them are much less dis- 
tinctly defined. 
(fg. 
os 
The base of the brain in the Echidna 
183) is remarkable for the deep and 
excavations at the under part of the anterior 
Fig. 183. 
Base of brain of Echidna. ( Original.) 
lobes, forming the base of the enormous 
olfactory nerves. The natiform rh gecesi 
are unusually large. The medulla oblongata 
is broad and flat, but contracted anteriorly to 
an angle; the pyramidal bodies (a) long and 
narrow ; the olivary bodies (6) broad, but flat. 
The pons Varolii (c) presents, as in the Orni- 
thorhynchus, a low development proportion- 
ally to the size of the brain: it is not raised 
beyond the level of the under surface of the 
medulla oblongata: it is of a triangular form 
with the obtuse apex turned forwards: the 
median longitudinal groove formed by the ba- 
silar artery is well marked : the trapezoid bodies 
are relatively narrower than in the Ornitho- 
rhynchus. 
The pituitary gland (p, fig. 183) is one line 
and a half in length and one line in breadth: 
its under surface adheres closely to the dura 
mater of the sella turcica. The corpus mam- 
MONOTREMATA. 
millare is single, broad, and but little ele- 
vated. : ¢ 
The internal, superior, and posterior walls 
of the lateral ventricle are from one line to two — 
lines in thickness ; the outer wall is between 
two and three lines; when the roof of the 
ventricle is removed, as in fig. 184, two 
elongated convex bodies exposed, as pe 
the marsupial brain: posterior 
largest (h) is the hip- i 
pocampus major: the Fig. 184. 
anterior body (s) is A 
the corpus striatum. “ye 
The whole internal 
wall of one ventricle 
is quite disunited from 
that of the opposite 
hemisphere.* 
The contracted an- 
terior parts of the hip- 
pocampi are connected 
together by the short 
transverse commissure 
above mentioned, 
which is the sole re- 
presentative of the cor- 
pus callosum and for- 
nix. Theseptum luci- Right lateral ventricle laid 
dum and fifth ventricle vO Echidna. 
are entirely absent. “— 
The pia mater, which accompanies the ven- 
tricular artery into the floor of the ventricle, 
at the base of the hippocampus, s over 
the optic thalami, and sends up a 
fold of membrane, one line and a half broad, 
between the hip pus and the —— 
striatum. The free margin of this fold is 
slightly thickened by the choroid artery. . 
t is necessary to remove the hippocampus 
re, in order 
i and bige~ 
and posterior of the hemis 
to bring into view the optic 
182, 2) and nates 
minal bodies. 
The optic thalami (fe. 
appear as one convex body slightly contracted 
laterally, and divided from each other by a si 
moid linear fissure: the testes are only half the 
breadth of the nates, and the median longiietians 
line of division, which is very faint in the larger 
bodies, is not visible in the smaller and pos- 
terior tubercle. The Echidna py in 
this characteristic modification with Orni- 
thorhynchus.t 
- 
* The internal structure of the hemi 
of 
the Echidna’s brain is not described in the* Voyage — 
~ 
de la Favorite.’ 
+ MM. Eydoux and Laurent have thrown into 
the following tabular form the published results 
of the dissections of the brains the 
cental Mammalia as compared with P. 
Mammals and Birds. 
pes MONODELPHEsS, DIDELPHES. OrniTHODELPHEs. | OISEAUX. | a) 
Corps calleuxr .... existe. manque. manque. manque. 
Pont de Varole . . existe. existe. existe. manque. 
Lobes optiques .. .| quadrijumeaux et | quadrijumeaux et bijumeaux et bijumeaux et 
supérieures. supérieures. supérieures, lateraux, =| 
They add: ‘‘ En indiquant ce résultat des ob- 
servations de M, R, Owen, aux-quelles nous avons 
joint les observations de Meckel en les 
nous devons faire remarquer que Stocks! 2 eopamen 
: 
| 
