MONOTREMATA. 
The transversalis cervicis and trachelo-mas- 
toideus are blended into a single oblong muscle 
arising from the anterior dorsal and the trans- 
verse processes of the six lower cervical ver- 
tebre, and inserted into the mastoid process. 
The sterno-mastoid is a double muscle on 
both sides, one portion being superficial (8), 
the other deep-seated; each arises separately 
from the episternal bone, and is separately 
inserted into the mastoid tubercle, behind the 
tympanic cavity. The omo-hyoideus and mylo- 
“ppg (10, 10) have a common insertion into 
eos hyoides. A muscle (1”), arising from 
the hyoid bone and expanding to be inserted 
into the lower lip, serves to retract this part. 
The sterno-hyoideus (11) joins the hyo-glossus. 
The genio-hyoideus (12) and the stylo-hyoideus 
(13) have the normal relations: the biventer 
maxille (14) is a short thick muscle, inserted 
near the bend, representing the angle, of the 
aw. 
The caudal muscles are powerfully developed. 
The oblique fibres of the inferior or deflector 
muscles are shown at 53; they are removed on 
the other side to expose the anterior caudal 
nerves (i). The obliguus externus abdominis 
(3, 3) arises from all the vertebral ribs, except 
the first, and from the dilated extremity of the 
ilium; it is inserted by a strong tendon into 
the outer extremity of the marsupial bone (vr), 
then expands into an aponeurosis which is 
attached to the internal margin and base of the 
marsupial bone, and into the symphysis pubis, 
decussating with the tendinous Apres of the 
opposite muscle. 
e obliquus internus (6) arises from the 
anterior part of the ilium, expands, and is 
inserted into the broad cartilages of the seven 
posterior ribs (v, v). 
The ¢transversus abdominis (7) is a thicker 
muscle, and arises from both the ilium and the 
transverse processes of the lumbar vertebre ; 
its tendon passes behind the recti to blend with 
_ that of the opposite muscle, and with the 
aia of the obliqui externi, in the linea 
The pyramidalis, or superficial rectus (4), is 
here, as in the ordinary Marsupials, of very 
large size; it arises from the whole inner margin 
of the marsupial bone ; its fibres converge to- 
wards and are confluent at the linea alba with 
those of its fellow, and it gradually terminates 
in a point opposite the posterior part of the 
sternum. It depresses the ribs, shortens the 
abdomen, and protracts the marsupial bone. 
The rectus abdominis, or posterior rectus (5), 
arises from the posterior margin of the marsu- 
pial bone, and is inserted into the cartilage of 
the first rib, the manubrium sterni, and the 
coracoid bone. 
_ The diaphragm presents the structure which 
is characteristic of the true mammiferous ani- 
Mal. The lesser muscle arises from the first 
lumbar and four last dorsal vertebre, and ex- 
pands to be inserted into the central tendon, 
which chiefly receives the fibres of the greater 
‘Muscle arising from the cartilages of the eleven 
inferior pairs of ribs. 
The pectoralis (2) is of very striking dimen- 
381 
sions; the origin of the superficial portion 
extends from the acromion, along the sternum 
and linea alba, almost to the pubis; a deeper- 
seated portion arises from the six osseous 
sternal ribs; the fibres of both portions con- 
verge to be inserted into the largely-developed 
pectoral or anterior crest of the proximal half 
of the humerus. 2 
The pectoralis minor is attached to the cora- 
coid, and the subclavius is likewise inserted, 
as in some other quadrupeds, into this bone, 
which is no longer a subordinate process of the 
scapula in the Monotremes. 
e subscapularis is a narrow muscle, and 
narrower in reality than at first sight it appears 
to be, since the supra-spinatus, from the inflec- 
tion of the spine and acromion, arises from the 
same aspect of the scapula, and appears to 
form the anterior fasciculus of the subscapularis ; 
its distinct insertion into the anterior tubercle 
of the head of the humerus points out its true 
nature. 
The infra-spinatus (20) and the large teres 
major cover the whole external surface of the 
scapula. 
e deltoid is divided into an anterior and 
a posterior portion. The anterior portion (19) 
arises from the anterior extremity of the cora- 
coid, and is inserted into the summit of the 
deltoid crest of the humerus: the posterior 
part (21) arises from the anterior and superior 
apex of the scapula, and is inserted into the 
lower half of the deltoid crest. There are 
also two muscles to which the name coraco- 
brachialis may be applied, a superior one (22) 
and an inferior one (25). 
The biceps brachii arises by two heads ; one 
(23) arises from the sternal extremity of the 
coracoid, the other (24) also arises from the 
coracoid ; the common tendon is inserted into 
the middle of the radius. 
The other muscles of the anterior extremity 
adhere closely to the mammalian type. The 
extensor carpi radialis (30) sends three ten- 
dons, to be inserted respectively into the second, 
third, and fourth metacarpal bones. There is 
a single common flexor digitorum, as well as 
extensor digitorum (27). 
The extensor digiti minimi (26), the indica- 
tor (28), the extensor pollicis (29), the prona- 
tor teres (32), and the flexor carpi radialis (33) 
are all remarkable for their strength in the 
Ornithorhynchus, and are still more powerfully 
developed in the Echidna. 
The most remarkable muscle on the palmar 
aspect of the fore arm is the fleror carpi ulnaris, 
which arises by two separate heads, the longer 
one from the broad olecranon, the shorter one 
from the internal condyle of the humerus; the 
common tendon is attached to the os pisiforme 
and the metacarpals of the fourth and _ fifth 
digits. 
The psoas minor from its insertion into the 
pelvic arch should be regarded as a muscle of 
the pelvic extremity, and it is one of the largest 
of thes muscles. It arises from the sides of 
five dorsal vertebra, and its strong tendon is 
implanted in the remarkably-developed ilio- 
pectineal process. It depresses the pelvis, 
