cartilage of the first rib, the manubrium sterni, and the coracoid bone.

The diaphragm presents the structure which is characteristic of the true mammiferous animal. The lesser muscle arises from the first lumbar and four last dorsal vertebræ, and expands 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 dimensions; the origin of the superficial portion extends from the acromion and episternum, along the sternum and linea alba, almost to the pubis; a deeperseated portion arises from the six osseous sternal ribs; the fibres of both portions converge to be inserted into the largely-developed pectoral or anterior crest of the proximal half of the humerus.

The pectoralis minor is attached to the coracoid, 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.

The subscapularis is a narrow muscle, and narrower in reality than at first sight it appears to be, since the supraspinatus, from the inflection 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 infraspinatus, 20, and the large teres major cover the whole external surface of the scapula.

The deltoid is divided into an anterior and a posterior portion. The anterior portion, 19, arises from the anterior extremity of the coracoid, 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 tendons, 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 indicator, 28, the extensor

pollicis, 29, the pronator 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 flexor 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 magna and iliacus internus form a single muscle, having the usual origins, and inserted by a common tendon into the large internal trochanter.

The psoas minor is the largest of these muscles. It arises from the sides of five dorsal vertebræ, and its strong tendon is implanted in the remarkably developed ilio-pectineal process. It depresses the pelvis, and with it also the tail and the pelvic extremities.

The ectogluteus is larger than is usually the case with quadrupeds; its insertion extends to the plantar fascia and the bone which supports the spur. The mesogluteus, entogluteus, pectineus, 45, biceps flexor cruris, gracilis, 34, sartorius, 35, rectus femoris, 36, adductores femoris, 46, semitendinosus, 47, semi-membranosus, vastus externus, offer no notable deviations from the usual structure. A strip of fibres, 49, descends from the gracilis to the sphincter cloacæ, H. A muscle, called by Meckel flexor accessorius a caudâ ad tibiam tendens,' 51, arises from the transverse processes of the anterior caudal vertebræ, 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 tibiæ; its fleshy belly passes across the sphincter cloacæ, H, and is connected with a strip of the panniculus carnosus, i.

The gastrocnemius, 48, derives its largest origin from the produced and expanded head of the fibula, and its smaller belly from the internal femoral condyle; its tendon is implanted in the calcaneum. The homotopy between the gastrocnemius and flexor carpi ulnaris is strikingly illustrated 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, extensor hallucis longus, 39, peroneus longus,

40, peroneus brevis, 41, extensor digitorum profundus, 42, extensor digitorum sublimis, 43, a portion of the same muscle corresponding with the indicator of the fore leg, and 44, extensor digiti quinti accessorius.

6

§ 194. Muscles of Marsupialia.-The most common posture of the Kangaroo is often termed the erect;' yet the conditions of this posture are very different from those in the human subject. The trunk, instead of resting upright on two nearly vertical pillars, is here swung upon the femora as upon two springs, which descend from the knee-joints obliquely backward to their points of attachment at the pelvis; and the trunk is propped up behind by the long and powerful tail, vol. ii., fig. 211.

In Man the massive and expanded muscles which find their attachment in the broad bones of the pelvis, especially at the posterior part, are the chief powers in maintaining the erect posture. But in the Kangaroo the glutei offer no corresponding predominance of size; the narrow prismatic ilia could not, in fact, afford them the requisite extent of fixed attachment.

The chief modifications of the muscular system in relation to the erect position of the trunk in the Kangaroo are met with on the anterior part of the base of the spinal column. The psoa parva, for example, present proportions the reverse of those that suggested their name in human anatomy. They form two thick, long, rounded masses, which take their origin, fleshy, from the sides of the bodies and base of the diapophyses of the lower dorsal and all the six lumbar vertebræ, and from the extremities of the three last ribs; the fibres converge penniformwise to a strong, round, middle tendon, inserted in the well-marked tubercle or spine of the pubis, already noticed.

The abdominal muscles include a pyramidalis as remarkably developed as in the Monotremes. In the Phalanger, fig. 4, the external oblique, besides the usual origin by digitations from the ribs, also arises from the fascia lumborum; it is inserted fleshy into the summit of the marsupial bone, a, over which its strong inner tendon is spread: the external oblique becomes aponeurotic at a line continued from the marsupial bone outward, with a gentle curve, toward the anterior extremity of the ilium; and in the opposite direction, or inward, the carneous fibres of the external oblique terminate in an aponeurosis along a line parallel with the oblique outer margin of the pyramidalis; the fascia continued from the latter boundary of the fleshy fibres passes over, or dermad of, that muscle, and meets its fellow at the linea alba; it is homologous

with the anterior layer of the sheath of the rectus in ordinary Mammalia. It is seen reflected from the pyramidalis, at b, fig. 4. The aponeurosis continued from the external and inferior boundary of the

carneous fibres divides as usual into two distinct portions. One, a, corresponding to the internal or mesial pillar of the abdominal ring, spreads its glistening fibres, as above described, over the dermal surface of the marsupial bone, c, to which it closely adheres: the other column, d, contracts as it descends obliquely inward, forms, like 'Poupart's ligament,' the upper boundary of the space

through which the psoas and iliacus muscles and femoral vessels and nerves escape from the pelvis, and is finally inserted, thick and strong, into the outer end of the base of the marsupial bone.

This bone is so connected with the pubis that its movements are almost limited to directions forward and backward, or those concerned with the dilatation and diminution of the abdominal space; the contraction of the abdominal muscles must draw the bones inward so as to compress the contents of the abdomen, and so far as the connections of the bone permit, which is to a very trifling degree, the external oblique may draw it outward toward the ilium. In some Marsupials, as the Koala, the triceps adductor femoris sends a slip of fibres to the external angle of the base of the marsupial bone, and would more directly tend to bend that bone outward.

The upper or anterior fibres of the internal oblique have the usual origin; the lower ones, e, arise fleshy from the outer and anterior spine of the ilium, and for an inch along an aponeurotic chord extended from that process to the upper part of the acetabulum: these carneous fibres pass inward and slightly upward, and terminate close to the outer margin of the rectus, where they adhere very strongly to the transversalis, but give off a separate sheet of thin aponeurosis which is lost in the cellular sheath of the posterior rectus.

The fleshy fibres of the transversalis abdominis, f, are closely connected by dense cellular tissue with those of the internal oblique; they are arranged in finer fasciculi, and have, as usual, a more transverse direction; they terminate along the same line as those of the internal oblique in an aponeurosis, g, which is continued along the inner or central surface of the posterior rectus to the median line. The lower boundary of the fleshy fibres of the transversalis is parallel with the line extended transversely between the anterior extremities of the ilia; a fascia, less compact than an aponeurosis, is continued downward from this margin, and envelopes the cremaster and the constituents of the spermatic chord, as they pass outward and forward beneath the lower edge of the internal oblique.

The pyramidalis, h, arises from the whole inner or mesial margin of the marsupial bone, from which the fibres diverge, the lower ones passing transversely across the interspace of the bones, and meeting at a very fine raphé, or linea alba; while those fibres from the anterior ends of the marsupial bones gradually exchange their transverse direction for one obliquely forward. The breadth of each pyramidalis opposite the upper end of the marsupial bone is more than an inch, the thickness of the muscle one line.

The rectus abdominis, i, comes off from the pubis along the inner part of the strong ligamentous union of the broad base of the marsupial bone, and expands as it ascends until it attains the level of the ensiform cartilage, when it diminishes as it is inserted into the sternal extremities of the ribs reaching to the manubrium sterni and first rib in the Dasyures, as in the placental Carnivores. The slight indications of tendinous intersections are confined to the posterior or central superficies of the muscle.

The cremaster, k, in the Phalanger and Opossum, is not a fasciculus of fibres simply detached from the lower margin of the internal oblique or transversalis, but arises by a narrow though strong aponeurosis from the ilium, within and a little above the lower boundary of the internal oblique, with the fibres of which the course of the cremaster is not parallel; it might be considered as a part of the transversalis, but it is separated by the fascia above mentioned from the carneous part of that muscle. Having emerged from beneath the margin of the internal oblique, the cremaster escapes by the large elliptic abdominal ring, 1, bends round the marsupial bone near its free extremity, and expands upon the tunica vaginalis testis. In the female it has the same origin, course, and size, but spreads over the mammary glands at