transversely, convex vertically, in the Echidna ; 
it is hardly definable when the cartilage is 
separated from the bone; but the patella itself 
is well developed, and ossified in both Mono- 
tremes (fig. 173, a, p). 
The tibia is straight in the Echidna, but 
bent, with the convexity next the fibula, in 
the Ornithorhynchus; its criste are slightly 
marked. 
The fibula is slightly bent in the Echidna, 
but is straight in the Ornithorhynchus ; in both 
Monotremes it is longer than the tibia by the 
extent of a process which rises upwards beyond 
_ the proximal articulation of the fibula, and 
most strongly expresses the analogy of this 
bone with the ulna: this process (fig.173, a, v) 
reaches half way up the back of the femur in 
the Ornithorhynchus, and, like the olecranon, is 
tly expanded at its termination. Cuvier* 
_ Indicates the resemblance of this structure in 
the Monotremes with the fibula and the super- 
numerary bone imposed upon its enlarged prox- 
imal end in the pedimanous Marsupials. 
The tarsus (figs. 178, 179) consists of a 
seaphoid (a), astragalus (b), a calcaneum (c), 
three cuneiform bones (d,e, f’), and a cuboid (g’) 
inthe Echidna; but the cuboid in the Ornitho- 
Fig. 178. 
Bones of hind-foot, Echidna hystrix. ( Cuvier.) 
_ thynchus is divided into two bones, as in some 
_ Reptiles, one for the fourth and the other for 
the fifth metatarsal bones. In both Mono- 
_ tremes there is a sesamoid bone (fig. 178, *) 
placed at the interspace between the astragalus 
and the naviculare; a second supernumerary 
__ bone (**) is articulated to the posterior part of 
_ the astragalus, and supports the perforated spur 
en characterizes the male sex (fig. 173, 
‘ q K, . 
The calcaneum of the Ornithorhynchus ter- 
_ Minates by sending outwards a short obtuse 
tuberosity ; in the Echidna this part is more 
Slender, and is singularly directed inwards 
* Ossem. Foss. v. pt. i. p. 153. 
MONOTREMATA. 
379 
and forwards, nearly in a line with the digits 
(fig. 179, e). 
The astragalus in the 
Ornithorhynchus pre- 
sents a double trochlea 
above for the tibia and 
fibula, and a depres- 
sion on its inner side, 
which receives the in- 
curved malleolus of the 
tibia, almost as in the 
Sloths. The toes have 
the same number of 
bonesas in other Mam- 
malia; their size and 
form are more alike in 
the two Monotrema- 
tous genera than those /, 
of the fingers: the un- #7 
gual phalanges, like “ # 
the claws they support, 
are more curved than 
those on the fore foot, 
but like them they are 
perforated on their in- Bones of hind-foot, plantar 
ner and concave side aspect, Echidna setosa. 
(fig.179). ( Original. ) 
Fig. 179. 
OF THE MUSCULAR SYSTEM. 
The figure (180) here given from Meckel?* il- 
lustrates some of the most instructive peculiari- 
ties of the muscular system of the Ornithorhyn- 
chus. The animal is dissected from the ventral 
surface; the great cutaneous muscle, the ‘ pan- 
niculus carnosus’ (1), is reflected from the right 
side, and the deeper-seated muscles are shown 
on the left. The panniculus carnosus, which is 
remarkable for its thickness, encompasses nearly 
the whole body, adhering most firmly to the 
external skin, but separated from the subjacent 
muscles, especially where it covers the thorax, 
abdomen, the arm, and the thigh, by a copious 
and lax cellular tissue; and in the female, at 
the abdominal region, by the mammary glands. 
The fibres are chiefly longitudinal, but at the 
lower part of the neck become transverse. The 
obtuse posterior end of the muscle is attached 
by three or four fasciculi to the dorsal aspect 
of the transverse processes of the caudal 
vertebre. The legs and the arms protrude 
through oblique apertures in this muscular 
tunic; some of the anterior fasciculi are in- 
serted by a short tendon into the pectoral ridge 
of the humerus; and others, still more anterior, 
are attached to the cranium, the lower jaw, and 
lower lip. A strip of fibres, which is cut off 
at 1*, is attached to the os hyoides; another 
fasciculus (1’) spreads over the cheek-pouch, 
ah assists in emptying that receptacle of the 
ood. 
The trapezius (9) is divided into two muscles; 
the posterior portion is an oblong slender tri- 
angle arising by a broad tendon from the tenth 
and eleventh vertebre and ribs, and inserted by 
a short strong tendon in the anterior extremity 
of the spine of the scapula; the anterior portion 
is shorter, but broader, and is subquadrangular; 
it arises from the occiput and tendinous raphé 
* De Ornithorhyncho, &c. tab. v. 
