382 
and with it also the tail and the pelvic extre- 
mities. 
The psoas magnus and iliacus internus form 
a single muscle, having the usual origins, and 
inserted by a common tendon into the large 
internal condyle. 
The gluteus externus is larger than is usually 
the case with quadrupeds; its tendon is inserted 
into the plantar fascia and the bone which sup- 
the spur. The gluteus medius, gluteus 
internus, pectineus (45), biceps flexor cruris, 
gracilis (34), sartorius (35), rectus femoris (36), 
adductores femoris (46), semitendinosus (47), 
semimembranosus, vastus externus, offer no 
notable deviations from the usua! structure. A 
strip of fibres (49) descends from the gracilis to 
the sphincter cloace (H). A muscle, called by 
Meckel ‘ flexor accessorius a cauda ad tibiam 
tendens’ (54), arises from the transverse pro- 
cesses of the anterior caudal vertebra, and 
converges to be inserted into the tibia. Another 
peculiar adductor of the leg, which might be 
termed ‘ intertibialis’ (52), is attached by its 
extremities to both tibie; its fleshy belly passes 
across the sphincter cloacee (H), and is connected 
with a strip of the panniculus carnosus (#). 
The gastrocnemius (48) derives its largest 
origin from the produced and expanded head of 
the fibula, and its smaller belly trom the internal 
femoral condyle; its tendon is implanted in the 
caleaneum. The analogy between the gastro- 
cnemius and ulnaris internus is strikingly illus- 
trated in the Ornithorhynchus. 
The soleus arises from the head of the fibula 
and from a large proportion of the tibia; it is 
nowhere blended with the gastrocnemius, but 
is inserted by a thick and short tendon into the 
astragalus. 
The abductors of the outer digits of both 
the hand and foot are well developed for the 
purpose of expanding the web which connects 
the toes. 
In the figure the following muscles of the 
leg are shown, viz. 37, tibialis anticus, 38, ex- 
tensor hallucis longus, 39, peroneus longus, 
40, peroneus brevis, 41, extensor digitorum 
communis profundus, brevi analogus, 42, exten- 
sor digitorum communis sublimis, 43, a portion 
of the same muscle corresponding with the 
indicator of the fore leg, 44, ertensor digiti 
quinti accessorius. 
NERVOUS SYSTEM. 
Brain.—In the male Ornithorhynchus 
Meckel found that the brain weighed two 
drachms, German weight (about four drachms 
avoirdupoise), and bore a proportion to the 
weight of the body as 1 to 130. It was in- 
closed by a pretty strong dura mater, of which 
the fold corresponding with the bony falx ad- 
hered but slightly to that process. The cere- 
brum weighed one drachm and a half, German; 
neatly the whole of its superficies was smooth ; 
a few vascular impressions marked the side of 
the anterior lobe: its shape was triangular, 
depressed; the contracted anterior lobes form- 
ing the obtuse apex of the triangle: the pos- 
terior lobes are wide and cover the corpora 
bigemina. The surface of the cerebrum is 
smooth and unconvoluted (fig. 181). 
MONOTREMATA. 
Silo vou en have of bree cee 
In describing the structure of the cerebral 
hemispheres Meckel observes, with ence 
to the most characteristic part of this ! 
in the Mammalia, “ us callosum ade: 
quidem, sed breve, quam haud quatuor line 
longitudine equet, memorabilius etiam 
in dimidia duo lateralia, linea mediana h 
confluentia, esse disjunctum. Equidem : 
tem in faciebus sese spectantibts internis nul- 
dete ACRNCle ea invenire potui.”— 
-c. p. 33. o 
During my investigations of the structure of 
the brain in the Marsupial err 
in memory the apparent exception to the ! 
like condition ‘of the co of calls wh 
the Ornithorhynchus, according to the above — 
description, presented, but which each suc- 
cessive example of the brain of the Marsupial — 
uadruped served to establish more firmly as — 
rule of structure in the higher order of t 
Implacental sub-class. It was difficult t 
believe that in the lower or M atous 
group, the cerebral organ, which indicates so 
accurately the true affinities and natural posi- 
tion of the Vertebrate animal, and which fe 
lows so faithfully the degradation of the general 
organization of each species, should offer so 
abrupt an ascent to the cerebral condition of 
the placental Mammalia, as would be indi- 
eated by a corpus callosum of four limes long 
in a brain of which the hemispheres measure 
only fourteen lines in length (German se 
The strong suspicion of an error in the cel 
biated anatomist’s description justified a re= 
serve in acknowledging this exception until 
the opportunity of testing it by a disse 
of a brain of a Monotrematous qui 
should have presented itself; and my 
as to the great development of the ¢ 
callosum of the Ornithorhynchus were furt 
justified by the indication of its nearer 
proach to the Oviparous type afforded t 
simple bipartite condition of the tubere 
* Philos. Trans. 1837, p. 87. 
