404 PROF. OWEN ON THE OSTEOLOGY 
the cremaster muscle winds round them in its passage to the testicle or mammary 
gland. 
The osteogenesis of the marsupial pelvis derives 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 Mam- 
malia, with a certain latitude of altered place and form, disguised, e. g. as the bone of 
the penis in the Carnivora, &c., or appearing as the supplemental ossicles of the aceta- 
bulum, which exist in the young of many of the Rodentia. In the os innominatum of an 
immature Potoroo it will be seen that the curved prismatic 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 ischiwm and pubis, excepting a small 
part of the under or mesial margin, which is formed by a distinct ossicle or epiphysis 
of the ilium, analogous to that described by Geoffroy St. Hilaire as the rudimental 
marsupial bone in the Rabbit. Now here there is a coexisting marsupial bone ; but 
besides the five separate bones just mentioned, there is a sixth distinct triangular ossi- 
cle, which is wedged into the posterior interspace of the ischio-pubic symphysis. How 
easy were it to suggest that this single symmetrical bone may be the representative of 
the os penis, removed from the glans to the root of the intromittent organ! I regard it 
as a mere epiphysis of the ischium. The circumference of the acetabulum is always in- 
terrupted by a deep notch opposite the obturator foramen, which is traversed by a liga- 
mentous bridge, and gives passage to the vessels of the Harderian gland lodged in the 
wide and deep acetabular fossa. 
The femur is a straight, or nearly straight, long cylindrical bone, having a hemisphe- 
rical head, supported on a very short neck, especially in the Petaurists, and situated 
here almost in the axis of the shaft, above and between the two trochanters, which are 
nearly of equal size. In the Kangaroos and Potoroos the head of the thigh-bone is 
turned more inwards, and the outer or great trochanter rises above it. In other 
Marsupials the great trochanter is less developed. In all the species a strong ridge is 
continued downwards, to a short distance from the trochanter; and this ridge is so 
produced at the lower part in the Wombat, as almost to merit the name of a third tro- 
chanter. 
In the Wombat and Koala there is no depression for a ligamentum teres. 
The shaft of the bone presents no linee aspere. The canal for the nutrient artery 
commences at the upper third and posterior part of the bone in the Koala, and extends 
downwards, contrariwise to that in most other Mammalia. At the distal extremity of 
the femur the external condyle is the largest, the internal rather the longest. The in- 
termediate anterior groove for the patella is well marked in the Perameles, where the 
patella is fully developed, but is broad and very shallow in the Phalangers and Dasyures, 
where the tendon of the rectus muscle is merely thickened, or offers only a few irregular 
specks of ossification; and the corresponding surface in the Petaurists, Wombat and 
