Fig. 119. 
Brain and spinal chord, Mapropus penicillatus. 
grey matter enveloping the central medullary 
tract in each lateral moiety of the chord is 
shewn in the three situations marked 1, 2, and 
3 (fig. 119); the superior expansion and com- 
plexity of the grey matter in the anterior 
columns of the pelvic enlargement accords 
with the predominance of the locomotive over 
the sensitive function* in the strong saltatory 
hind legs of the Kangaroo. 
Organs of Sense —The olfactory nerves and 
the osseous cavities and lamine destined for 
the protection and support of the pituitary 
membrane offer a remarkable proportional 
development in all the Marsupials, and more 
especially in the Insectivorous and Carnivorous 
tribes. e outer root of the olfactory nerve 
appears as a continuation of the whole nati- 
form protruberance ; a corresponding accumu- 
lation of nervous matter,“ protuberantia py- 
riformis,” + at the base of the inner root of 
the olfactory nerve has already been noticed ; 
both these broad tracts consist externally of 
grey matter: the middle or medullary root of 
the nerve is the smallest. It is very con~ 
spicuous in the Wombat, where it emerges 
from a longitudinal fissure at the anterior and 
inner of the “ protuberantia natiformis.” 
The ol nerves or rather lobes are hollow, 
and contain, as in most Mammalia, the ante- 
* Mayo, Outlines of Physiol p. 238, 
Phil. Trans. 1837, p. 95.” 
MARSUPIALIA. g 
rior continuation or extremity of the lateral 
ventricles (0, fig. 118). The filaments pass 
from the skull through several foramina of a 
cribriform plate. Certain species of Kangaroo, 
of the subgenus Osphranter, Gould, remarkabl 
for theiracuteness of ae urbinated 
bones so large that the lateral expansion of th 
nasal cavity forms a marked feature in the skul 
The chief deviation from the Mam 
type in the orgun of hearing presents itse 
the form of the stapes, the body of ‘ 
a simple elongated style either entirely, a 
the saad ‘is for seo its : as 
the Kangaroo (fig. 120), where it divides int 
two short crura, before ter- 
minating in the base ; it us 
i 
Fig. 120. 
more or less approximates 
Ne 3 _ the form of the col nella in 
€@& the bird. 
The largest proporti 
Stapes of the Kan- external ears are those of the 
Free Perameles lagotis, the short 
est those of the Wombat. The internal struc- 
ture of the ear is not less strikingly develope: 
in the Perameles than the oa appendages 
The tympanic cavity is very extensive, but is 
formed, as in other Marsupials, by the sph 
noid and petrous bones; the tympanic bong 
is limited to the function of supporting the 
ear-drum, and forming the inte 
ment of the meatus auditorius externus. Th 
internal extremity of the tympanic cylinder 
projects obliquely into the posterior and outer 
part of the sphenoidal bulla. The membrana 
tympari is a delicate transparent tissu 
slightly concave internally, and having the 
long handle of the malleus (a, fig. 121) at- 
tached to it. This pro- 
cess of the malleus is bent 
upon itself at a right an 
a the inner portion is 
broader and thicker than 
that which is attached to 
the membrana tympani, 
and it is anchylosed at i 
internal extremity by < 
thin and tran it plate 
of bone (6) to the si 
of the incus (ce). T 
little ossicle, which here 
appears as a process - 
che malleus, presents 
notched articular surface for the orbicular end 
of the stapes. This portion of the stapes gives 
off a short slender process for the attachment of 
the stapedius (d ), and then is continued in the 
form of a moderately long and slender colamel- 
liform shaft to the elliptical and slightly ex- 
panded base which closes the foramen ovale. — 
Organ of Vision—The anatomy of the eye 
offers no peculiarity illustrative of the affinities _ 
of the Marsupialia or of any other speciality in 
their economy save the nocturnal habits of the 
majority of the order. It is in relation to these — 
habits that the lens is large and convex, the 
iris broad, the pupil round and generally wide, 
and the cornea pega 9 pare large. Cy 
The Harderian gland and the retractor oculi 
co-exist, as vrenat in Mammalia, with the — 
nictitating eyelid. This is always largely de~ 
COULD 
Fig, 121. 
rs 
Auditory ossicles, 
Perumeles. 
