In claviculate marsupials the deltoid is larger, and consists of three fasciculi.

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.

The pectoralis major is, as usual in the Marsupial and many higher quadrupeds, a 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 converge, increasing in thickness as they diminish in breadth, and are inserted into the anterior and outer part of the strongly developed 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 pectoral pass obliquely upward and behind the anterior fasciculi, and are inserted into the coracoid process, thus representing the pectoralis minor. Beneath this latter portion of the 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 as a 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 vertebræ 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 suppressed. 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, while the inner tendon bends and pronates; the latter, which is a direct though partial continuation of the biceps, is inserted into the ordinary tubercle of the radius; whereas the outer tendon is attached to the fore part of the proximal end of the ulna. The muscles which arise from the internal condyle of the humerus are the pronator teres, which has the usual origin, insertion, and relative proportions, and next a large palmaris longus. There are, likewise distinct and strong fasciculi of muscles corresponding to the flexores carpi ulnaris and radialis, and to the flexor sublimis digitorum. The strong ridge continued from the olecranon to the posterior and inner part of the ulna gives origin to a great proportion of the oblique fibres of the flexor profundus; but both this and the flexor sublimis terminate in a single thick and strong tendon, which after passing the wrist divides into those corresponding with the perforating and perforated tendons concentrated, in Perameles, upon the three long middle fingers. The pronator quadratus runs the whole length of the interosseous space, passing from the radius a little obliquely downward to the ulna. The supinator longus, arising as usual from the upper part of the strongly developed ridge above the outer condyle, sends its tendon across the carpal joint, which tendon divides before it crosses, and is inserted by one of its divisions into the base of one of the metacarpal bones of the index finger, and by the other into the adjoining metacarpal bone.

These are the principal muscles of the fore extremity which require notice. Their modifications, in respect of number and strength, relate to the act of digging up the soil, which is habitual in the Bandicoots, as it is for the purpose of obtaining food, and not for shelter. It is for this purpose that the three middle digits of the hand are developed at the expense of the other two, which are rudimental; the whole power of the deep and superficial flexors is concentrated upon the fossorial and well-armed fingers; and, by the single common tendon in which the fleshy fibres of these muscles terminate, they move them collectively and simultaneously. Thus variety of application, and especially the prehensile faculty, are sacrificed to the acquisition of force for the essential action. In no Marsupial is the hand so cramped as in the Perameles, excepting in the Charopus, where the functional and fossorial fingers are reduced from three to two. It is in relation to this condition, doubtless, that the clavicles are wanting in these genera, while all other Marsupials possess them. In these

the biceps has the usual two origins: the flexor sublimis digitorum is distinct from the flexor profundus in Didelphys.

The muscles of the hinder extremity are chiefly remarkable in the Kangaroo for their prodigious strength and unusual number: the accessory muscle of the biceps cruris, e. g., arises from a caudal vertebra, and, with that from the ischium, forms two strong fasciculi, one inserted into the outer femoral condyle, the other into fascia covering the gastrocnemii. The pyriformis is also a double muscle. The sartorius has its insertion so modified that it becomes an extensor instead of a flexor of the tibia: it is chiefly fixed to the tibial side of the gristly patella, and by fascia into the capsular ligament of the knee-joint and the anterior proximal tuberosity of the tibia. In a Dasyure (Das. macrurus) I found that the sartorius had a similar disposition and office. In this ambulatory carnivorous Marsupial the external and middle glutai are so disposed as to extend the thigh, while the internal glutaus inflects and rotates it inward. In a Bandicoot (Perameles lagotis) the sartorius ran nearly parallel with and dermad of the rectus, and was inserted into the upper part of the patella. Besides this sesamoid, which is rarely developed in other Marsupials, I found a thick cartilage attached to its upper part and interposed between the common tendon of the recti and vasti, removing that tendon further from the centre of motion, and increasing the power of the extensor muscles of the leg. The rectus femoris has its two origins very distinct, and its homotypy with the biceps of the upper extremity is obvious. The gracilis is a very thick and strong muscle. The biceps flexor cruris in the Perameles is a muscle of very great strength; it terminates in a strong and broad aponeurosis, which extends over the whole anterior part of the tibia, being attached to the rotular tuberosity of that bone, and terminating below in the sheath of the tendo Achillis, whereby this muscle becomes an extensor of the foot.

All the equipedal Marsupials, whether burrowers as the Wombat, climbers as the Koala, Phalangers, and Opossums, or simply gressorial, as the Dasyurida, have the tibia and fibula so connected together as to allow of a certain degree of rotation upon each other, analogous to the pronatory and supinatory movements of the bones of the antibrachium, and the muscles of the leg present corresponding modifications. None of the analogous carnivorous, pedimanous, or rodent Placentals present this condition of the hind leg. In the Kangaroo, the gastrocnemii almost rival those of Man in the bulk of the fleshy part.

In the Dasyurus macrurus, the plantaris, instead of rising from

the femur, has its fixed point in the fibula, from the head to halfway down the bone, fleshy; its tendon passes obliquely inward, and glides behind the inner malleolus to its insertion in the plantar fascia, so that it rotates the tibia inward besides extending the foot. The soleus has an extensive origin from the proximal to near the distal end of the fibula. There are, as usual, three deepseated muscles at the back of the leg. Of these three the muscle homologous with the tibialis posticus is readily recognised; its tendon glides behind the inner malleolus, and is inserted into the inner or tibial cuneiform bone.

5

The muscle which has the relative position and origins of the flexor longus pollicis, sends its tendon by the usual route to the sole of the foot, where it divides and distributes a flexor tendon to all the toes except the rudimental hallux; it has the same disposition in the Opossums, where the hinder thumb or great toe is fully developed for this modification, however, the Comparative Anatomist is already prepared by meeting with such common office of the muscle in the first step from Man, viz. in the Orang, Gorilia, and Chimpanzee.

The third deep-seated muscle, being situated internal to the two preceding ones, may be the homologue of the flexor digitorum communis longus; it nevertheless sends no tendon to the toes nor even to the tarsus, but its fibres pass from the tibia obliquely outward and downward between the preceding muscle and the interosseous ligament to the fibula, where they are exclusively inserted so as to

oppose the plantaris and rotate the foot outward. This muscle closely adheres to the intercsseous fascia, and thus resembles in its

attachments the pronator quadratus of the fore limb: it is most developed in the pedimanous climbing Marsupials, where the rotation of the foot is more frequent and extensive.

Fig. 5 shows this modification of the muscles of the hind-foot in the Phalangista vulpina; a, is the expanded tendon of the sartorius; b, gracilis; c, semitendinosus; and d, semimembranosus; both these muscles are inserted, as in many other quadrupeds, low down the tibia: e, gastrocnemius; f, plantaris; g, the homologue of the flexor longus pollicis pedis; h, tibialis posticus; this muscle divides and is inserted by two tendons, h' and h", into the internal and middle cuneiform bones; i, the rotator muscle of the tibia.

In the muscles on the anterior part of the leg, the extensor brevis digitorum has its origin extended into this region, and is attached to the outside of the fibula. There are three peronei; the external one is inserted into the proximal end of the fifth metatarsal: the tendon of the middle peroneus crosses the sole in a groove of the cuboid like the peroneus longus: the internal peroneus is an extensor of the outer or fifth toe. The Perameles lagotis, among the saltatorial Marsupials, presents a different condition of the extensors of the foot from that above described. The gastrocnemii, soleus, and plantaris all arise above the kneejoint, and the tendon of the plantaris, after sheathing the tendo Achillis and traversing the long sole, is finally inserted into the base of the metatarsal bone of the fourth or largest toe; thus this muscle, which is strongly developed, bends both this toe and the knee, while it extends the foot.

In the Kangaroo the flexor of the toes rises from the outer tuberosity of the tibia, its fleshy part covers the back of the leg beneath the soleus, the tendon passes to the sole and divides into a large tendon for the principal toe, fig. 211, iv, a smaller tendon for the outer toe, v, and a still smaller tendon which goes to the two slender inner toes. The muscle seems to combine the homologues of the flexor hallucis and flexor digitorum, with, perhaps, also that of the tibialis posticus.

§ 195. Muscles of Lissencephala.-The Rodentia closely resemble the Marsupialia in their muscular system; with like modifications according to the absence or presence of clavicles, and to the gradatory, saltatory, scansorial, and fossorial movements of the species respectively. They have not the marsupial modifications of the cremaster and abdominal muscles, nor the rotatory muscle of the tibia; but certain Rodents show peculiarities of the masseter which will be noticed in connection with the organs of mastication.