284 
foetuses that we ought to find auxiliary parts 
for increasing the tg of the muscles engaged 
in parturition, e bones in question are, 
moreover, equally developed in both sexes: 
and they are so situated and attached that they 
add to the power of the muscles which wind 
round them, and not of those implanted in 
them. They are not, however, merely sub- 
servient to add force to the action of the “ cre- 
masteres,” but give origin to a great proportion 
of the so-called “ pyramidales.” 
The osteogenesis of the marsupial pelvis de- 
rives some extrinsic interest from the not yet 
forgotten speculations which have been broached 
regarding the analogies of the marsupial bones. 
These have been conjectured to exist in many 
of the placental Mammalia, with a certain la- 
titude of altered place and form, disguised, 
€. g. as the bone of the penis in the Carnivora, 
or appearing as the supplemental ossicles of 
the acetabulum, which exist in the young of 
many of the Rodentia. In the os innomina- 
tum of the immature Potoroo the curved pris- 
matic ilium contributes to form, by the outer 
part of its base, the upper or anterior third of 
the acetabulum; the rest of the circumference 
of this cavity is completed by the ischium and 
pubis, excepting a small part of the under or 
mesial margin, which is formed by a distinct 
ossicle or epiphysis of the ilium, (a, fig. 110,) 
analogous to that de- 
scribed by Geoffroy St. 
Hilaireas the rudimen- 
tal marsupial bone in 
the rabbit. Now here 
there is a co-existing 
marsupial bone: but 
besides the five sepa- 
rate bones just men- 
tioned, there is a sixth 
distinct triangular ossi- 
cle, which is wedged 
into the posterior in- 
terspace of the ischio- 
pubic symphysis. How 
easy were it to suggest 
that this single sym- 
metrical bone may be 
the representative of 
the os penis removed 
from the glans to the 
‘2 root of the intromittent 
; organ! I regard it as 
a mere epiphysis of the 
ischium: The circumference of the acetabulum 
is always interrupted by a deep notch opposite 
the obturator foramen, which is traversed by 
a ligamentous bridge, and gives passage to 
the vessels of the Harderian gland lodged in 
the wide and deep acetabular fossa. 
The penial like the marsupial bone is essen- 
tially an ossification of the fibrous or sclerous 
tissue. 
The femur is a straight, or nearly straight, 
long, cylindrical bone, having a hemispherical 
head supported on a very short neck, espe- 
cially in the Petaurists, and situated here 
almost in the axis of the shaft, above and 
between the two trochanters, which are nearly 
Fig. 110. 
MARSUPIALIA. 
of equal size. In the Kangaroos and Potoroos 
the head of the thigh-bone is turned more 
inwards, and the outer or greater ter 
rises above it. In other Maes the great 
trochanter is less developed. In most of the 
species a strong ridge is continued down 
to within a short distance from the trochanter, 
and this ridge is so produced at the lower pai 
in the Wombat as almost to merit the name 
of a third trochanter. In the Wombat ; 
Koala there is no depression for a ligamentu 
teres. The shaft of the bone presents no ding 
aspere. ¥, 
The canal for the nutrient artery commences - 
at the upper third and posterior part of the 
bone in the Koala, and extends downward: 
contrariwise to that in most other ma 
and placental Mammalia. a 
At the distal extremity of the femur the 
external condyle 1s the largest, the internal 
rather the longest. The intermediate anterio 
groove for the patella is well marked in the 
Perameles, where the patella is fully developed, 
but is broad and very shallow in the Phalai 
gers and Dasyures, where the tendon of t 
rectus muscle is merely thickened or offers 
only a few irregular specks of ossification ; | 
the corresponding surface in the Petaurists 
Wombat, and Koala is almost plane from side 
to side; in these Marsupials and in the Myrme- 
cobius the patella is wanting. 1 find adistinet 
but small bouy patella in the Macropus E 
nettii. There is a sesamoid bone above and 
behind the external condyle of the femur in the 
Myrmecobius and some other Marsupials. J 
In the knee-joint, besides the two crucial 
ligaments continued from the posterior angles — 
or cresses of the semilunar cartilages—one to” 
the outer side of the inner condyle, the other 
to the interspace of the condyles—there isa 
strong ligament which passes from the anterior 
part of the tibial protuberance backwards 
the inner side of the fibular condyle, and a 
second continued from the same point along 
the outer margin of the outer semilunar ¢ 
tilage to the head of the tibia. 
The tibia (a, fig.111) presents the usual dis- 
position of the articular surface for the condyles 
of the femur, but in some genera, as the Wombat 
and Koala, the outer articular surface is continu- 
ous with that forthe head of the fibula. In the 
Kangaroos and Potoroos the anterior part of 
the head is much produced, and in the young 
animal its ossification conmmences by a centre 
distinct from the ordinary proximal epiphysis 
of the bone. A strong ridge is continu 
down from this protuberance for about or 
sixth the length of the tibia. In the Koalaa 
strong tuberosity projects from the anterior part 
of the tibia at the junction of the upper with — 
the middle third. In this species and in the — 
Wombat, as also in the Opossums, Dasyures, — 
Phalangers, and Petaurists, the shaft of the — 
tibia is somewhat compressed and twisted; 
but in the Kangaroos, Potoroos, and Pera-— 
meles the tibia is prismatic above and sub- 
cylindrical below. The internal malleolus is — 
very slightly produced in any Marsupial, but 
most so in the Wombat. : 
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