MARSUPIALIA. 
by the large elliptic abdominal ring (/), bends 
round the marsupial bone near its free ex- 
tremity, and expands upon the tunica vaginalis 
testis. In the female it has the same origin, 
course, and size, but spreads over the mam- 
mary glands at the back of the pouch. If the 
anterior fascicles of the diverging and em- 
bracing fibres be dissected from the posterior 
Ones, the appearance of the cremaster dividing 
into two layers is produced. 
The principal modifications of the muscles 
of the pectoral extremity are here described as 
ye: Seaore in the Perameles lagotis. 
trapezius is a broad and very thin mus- 
cle, having its origin extended from the skull, 
along the cervical and dorsal spines, to the 
fascia covering the lumbar portion of the latis- 
simus dorsi: its fibres converge to be inserted 
along the spine of the scapula, the anterior ones 
directly continued into the pectorales, whereby 
it becomes an extensor of the humerus and a 
protractor of the fore extremity. 
The Jatissimus dorsi arises chiefly from the 
broad aponeurosis covering the muscles of the 
lumbar region of the spine, and from the spines 
of the six posterior dorsal vertebre ; the fibres 
gradually converge, the muscle increasing in 
thickness as it diminishes in breadth, and 
terminating in a strong flattened tendon one 
inch before its insertion at the upper third of 
the humerus. 
The chief peculiarity of this muscle is its con- 
nection with an accessory extensor (omo-anco- 
neus) of the antibrachium. This extensor 
takes its principal origin by fleshy fibres from 
the terminal half inch of the fleshy part of the 
latissimus dorsi, and continues fleshy, slightly 
diminishing in size to its insertion at the apex 
of the olecranon; it may thus be considered as 
a slip detached from the latissimus dorsi, yet 
its fibres from their very origin run at right 
angles to those of that muscle, to which they are 
attached. To remedy the inconvenience of 
an origin from a yielding and flexible part, a 
thin aponeurotic slip, two lines in breadth and 
an inch in length, attaches a part of the base of 
the superadded muscle and the corresponding 
portion of the latissimus dorsi to the sheath of 
ihe teres major, and to the inferior costa of the 
scapula near its posterior angle. 
1e serratus magnus offers no peculiarity 
worthy of notice. 
The supra-spinatus, a strong penniform mus- 
cle, exceeds the infra-spinatus in breadth by as 
much as the supra-spinal fossa is broader than 
the infra-spinal one: it has a broad and strong 
insertion into the great outer tuberosity of the 
humerus. The infra-spinatus is inserted into 
the upper and posterior part of that tubero- 
sity. 
The deltoides is a comparatively small muscle ; 
it arises from the anterior half of the spine of the 
scapula and from a fine aponeurosis covering 
the infra-spinatus ; its fibres converge to be in- 
serted in the upper part of the deltoid ridge. 
A thin small strip of muscle arises from 
about the middle of the inferior costa of the 
scapula, beneath the infra-spinatus ; its fibres 
pass forwards and join the lower margin of the 
VOL. Ii. 
289 
small deltoid, thus bracing and enclosing the 
tendon of the infra-spinatus. 
The subscapularis offers no peculiarity. 
The teres major is a strong sub-compressed 
muscle arising from near the posterior half of 
the inferior costa of the scapula, and joining, as 
before stated, the tendon of the latissimus. 
The triceps extensor has its long portion 
arising from the anterior third of the inferior 
costa of the scapula; its second head comes 
from the posterior part of the proximal third of 
the humerus; the third portion takes its origin 
from the whole of the posterior part of the 
humerus ; in addition to these, the olecranon 
receives the above described fourth superadded 
slip from the latissimus dorsi. 
e pectoralis major is, as usual in the Mar- 
supial and many of the Placental quadrupeds, 
a very complicated muscle; it consists of an 
anterior or superficial, and a posterior or deeper 
portion ; the anterior portion receives the strip 
of fibres before mentioned from the trapezius, 
there being no clavicle or clavicular ossicle 
interposed in the Perameles: its fibres con- 
verge, increasing in thickness as they dimi- 
nish in breadth, and are inserted into the 
anterior .and outer part of the strongly deve- 
loped pectoral ridge. The second and main 
portion of; the pectoralis arises from the whole 
extent of the sternum; its fibres are twisted 
obliquely across each other as they converge 
to be inserted into the inner part of the pectoral 
ridge; some of the internal and posterior fibres 
of this portion of the twisted pen pass ob- 
liquely upwards and behind the anterior fasci- 
culi, and are inserted into the coracoid process, 
thus representing the pectoralis minor.* Be- 
neath this latter portion of the twisted pectoral, 
a long and slender muscle passes to be inserted 
into the anterior part of the tuberosity of the 
humerus; this may likewise be regarded asa 
dismemberment of the pectoralis major, but it 
arises from the fascia of the rectus abdominis, 
below the cartilages of the lower ribs. Thus 
the strong pectoral ridge of the humerus is 
acted upon by muscles having a range of origin 
from the occiput and cervical vertebre along 
the whole extent of the chest to the beginning 
of the abdomen. 
The biceps is a powerful muscle, although 
its short head from the coracoid process is sup- 
pressed. The long head has the usual origin 
and relation to the shoulder-joint; its tendon 
is very thick and short. The fleshy belly joins 
that of the strong brachialis internus, situated 
at the external side of the humerus, whence it 
takes its principal origin from the short deltoid 
ridge, closely connected there with the second 
portion of the triceps, and deriving some fleshy 
fibres from the lower and outer third of the 
humerus. The portion of the biceps arising 
by the long head soon resolves itself into two 
distinct penniform muscles ; the tendon of the 
outer one joins that of the brachialis, and this 
conjoined tendon simply bends the fore-arm, 
* Professor Vrolik found that the pectoralis 
minor in the Kangaroo was inserted not into the 
coracoid process, but into the humerus between the 
biceps and the tendon of the pectoralis major. 
U 
