378 
supporting the innermost digit or pollex, the 
trapezoides (g), the index, the os magnum (/’), 
which is almost the smallest, sustaining the 
medius, and the unciforme (e) the two outer 
digits: this description is taken from the 
Echidna: the only essential difference obser- 
vable in the Ornithorhynchus is the contribu- 
tion by the os magnum of a greater share to 
the articulation with the ring-finger. 
In the Echidna all the bones of the fore- 
extremity are relatively larger and stronger 
than in the Ornithorhynchus, but this dif- 
ference is especially remarkable in the meta- 
} bones and two first rows of phalanges 
Jig. 176, h, i, k), which are singularly short, 
broad, and thick. The palm is strengthened 
by two large sesamoids developed in the flexor 
tendons in the Echidna; these are sometimes 
confluent (fig. 175, 1). The number of pha- 
langes in both Monotremes is the same as in 
other Mammals, viz. two to the thumb and 
three to each of the fingers. This is not the 
case in any Saurian, and the retention of the 
Mammalian type at the peripheral segment of 
the limb, with the singular deviation from it at 
the central supporting arch, is not one of the 
least remarkable points in the osteology of the 
Monotremes. 
There is a sesamoid bone at the palmar 
aspect of each of the distal articulations of the 
phalanges in the Echidna (fig. 175), and at all 
the digital articulations in the Ornithorhynchus 
(fg. 173, u,d@). 
Fig. 176. 
Bones of the fore-foot, Echidna hystrix. 
The ungual phalanges are long, depressed, 
nearly straight, of great strength in the Echidna, 
in which each of them is perforated at the 
palmar aspect (fig. 175). 
Of the pelvic extremities.—The pelvis of the 
Monotremes bears a resemblance to that of 
Reptiles in the length of time during which 
the three components of each os innominatum 
remain distinct, especially in the Echidna; and 
in the great development of the ilio-pectineal 
spine, which equals in size that of the tortoise, 
MONOTREMATA. 
in the Ornithorhynchus; the pelvis of “ei 
Echidna resembles that of Birds in the we 
ration of the acetabulum (fig. 177, g), butthe 
pelvis in both Monotremes chiefly resembles 
that of the higher implacental Mammalia in 
the presence of the marsupial bones. see ; 
Fig. 177. . 
Re a es 
a oe 
a 
“ 
Internal view of pelvis, Echidna setosa. ; 
( Original. ) - 
The ilium (fig. 177, a) is a short, strong, 
trihedral bone, with the upper extremity ex- 
panded and everted in the Ornithorhynchus. 
he ischium (6) has its tuberosity prolonged 
backwards in an obtusely-pointed form in the 
Ornithorhynchus. The pubis in the same 
animal, besides having the spinous process 
directed forwards, gives off a second smaller 
process, which projects outwards; this s 
is present, but less developed in the Echidn 
(fig.177, f). The pubis (c) and ischium con- 
tribute an equal share to the formation of the 
foramen obturatorium (/) and to the symphysis 
which closes the pelvis below: the symphysis is 
relatively shorter in the Echidna (d) than in the 
Ornithorhynchus. mS 
The marsupial bones (fig. 173, A, 22, 177, €) { 
are relatively larger and score in the Mono- — 
tromes than in the ordinary Marsupialia, the 
Koala excepted; their base extends along the 
anterior margin of the pubis from the sy 
outwards to that of the spinous process 
177, f); they are relatively longer in the 
Echidna (e) than in the Ornithorhynehus; they — 
always remain moveably articulated with the 
brim of the pelvis. C2 a 
The femur is short, broad, and dane f 
head rises, like that of the humerus, from the — 
middle of a broad expanded proximal end, 
having on each side a strong process, the outer 
one representing the great, the inner one tl 
small trochanter. In the Echidna a project- 
ing ridge extends from the great or outer tro- 
chanter beyond the middle of the bone; the — 
whole of the inner part of the shaft is bounded — 
hy a trenchant edge; both outer and immer 
margins of the bone are trenchant in the 
Ornithorhynchus. The distal end of the femur — 
is expanded transversely, but com : 
before backwards. The rotular trochlea 
a 
