fibres from the deeper surface of the main tendon; 16 is the tendon to the last phalanx of the second toe.

The long fibular flexor of the toes, arising from the back part of the fibula and interosseous ligament, grooves by its tendon the posterior part of the tibia, the astragalus and the calcaneum, and divides at the sole, fig. 26, 2, into the perforating tendons of the hallux, 2c, the third, 26, and the fourth, 2a, toes. The portion of the flexor brevis which rises from the calcaneum divides into two tendons which form the perforated ones of the third, 3', and second, s", toes. The short muscles giving the grasping power to the hind thumb are, 8, abductor hallucis,' 9, flexor brevis hallucis,' 10 adductor obliquus hallucis,' and 11, 'adductor transversalis hallucis.' The lumbricales and interossei are powerfully developed. In the Orang the long fibular flexor sends no tendon to the hallux.

The ordinal modification of the hind- or lower- limbs for the whole work of sustaining and moving the body, in Bimana, is accompanied by well marked and considerable modifications of the toes, the chief of which are illustrated by comparison of the figure, 26, from the highest ape, with fig. 27. The long

fibular flexor now becomes the flexor longus hallucis,' and concentrates its force exclusively on the tendon, 2, 2c, which goes to the last phalanx of the hallux, i; this tendon is twice the size of any of the divisions of that of the long flexor on the tibial side. This is limited to the function implied by the name 'flexor longus digitorum pedis,' its tendon, fig. 27, 1, sending off successively the perforating tendons to the second, third, fourth, and fifth toes. In fig. 27, are shown the insertion of the 'tibialis posticus,' 15; the 'flexor brevis minimi digiti,' 7; the flexor brevis pollicis,' inserted into the outer, 9, and inner, 10, sesamoids, the adductor pollicis, 8, and the peculiar 'transversalis pedis,' 10, arising from the under surface of the distal and of the fifth metatarsal, crossing three of the other metatarsals, to be inserted into the outer side of the proximal phalanx of the hallux, blending there with that of the adductor pollicis.'

The heel being the lever-power by which the whole superincumbent weight of the body is raised in the peculiar walk,' or bipedal gait, of Man, muscles that are distinct in quadrupeds are here, contrary to ordinary rule, blended, or have a common insertion. Not only the outer and inner gastrocnemius, but the soleus, and even the plantaris, might be regarded as so many origins of the same muscle, which combine and concentrate their forces upon the calcaneum.

The 'panniculus carnosus' of quadrupeds is reduced in Bimana to the platysma myoides,' fig. 28, p, p, p, which extends from the upper and fore part of the chest upward over the front and side of the neck to the mandible and lower part of the face, where the two muscles meet below the symphysis. The middle fibres are attached to the base of the jaw, and posteriorly ascend to the fascia of the masseter; the anterior ones ascend with the depressor anguli oris and quadratus menti to the lower lip and angle of the mouth. In many instances there is a strip from the parotid fascia which converges to this angle, and constitutes the risorius santorini.' The platysma draws down the lower part of the face, or, by a slighter action, the lower lip: the risorial' slip tends to raise the angle of the mouth. Most of the muscles of the face are attached at one part to bone, at another to skin or to some other muscle. The skin of the human face is remarkable for its tenuity, flexibility, and abundant supply of vessels and nerves; its vascularity tinting the cheeks and lips: it is more adherent and the subjacent cellular tissue is denser along the median line than at other parts.

The orbicularis oris,' fig. 29, o o, has no attachment to bone.

It consists of two semi-elliptic planes of muscular fibres which surround the mouth and interlace on either side with those of the buccinator' and other dilators of the oral orifice. The external or peripheral surface adheres to the skin, the internal or posterior surface is covered by the mucous membrane of the mouth. Acting as a whole it closes the mouth, bringing the lips:

in contact and pressing them firmly together, but the upper and lower halves can act separately, or the fibres of one side may contract while the others are quiescent, so that different parts of the lips may be moved by different portions of the muscle, which may be regulated or antagonised by the muscles which converge to the mouth. A pair of accessory strips to the orbicularis, accessorii orbicularis superioris,' rise from the alveolar border of the premaxillary, and arching outward on each side are continuous at the angles of the mouth with the other muscles there inserted. A second pair,' naso-labiales,' descend from the septum of the nose to the upper lip, but with an interval, corresponding with the depression on the skin beneath that septum.

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The levator labii superioris,' fig. 29, 1, arises from the lower margin of the orbit, and descends to be inserted into the orbicularis and the skin of the upper lip. The 'levator anguli oris,' fig. 29, c, arises below the suborbital foramen and descends, inclining outward, to the angle of the mouth, blending its fibres with those of the zygomatici and orbicularis. The zygomaticus major,' fig. 29, 3, is cylindrical, rising from the malar and descending obliquely inward to a similar insertion at the angle of the mouth. The zygomaticus minor, fig. 29, 3, arises in front of the zyg. major, and passing downward and inward to the angle of the mouth, where it is continuous with the outer margin of the levator labii superioris. The levator menti is a conical fasciculus. arising from the incisive fossa of the mandible, external to the symphysis, and expanding as it descends to be inserted into the integument of the skin. The depressor labii inferioris,' fig. 30, d, arises from the inner half of the external oblique line of the mandible, and is partly also continued from the platysma: its fibres ascend, inclining inward to be attached to the lip, where they blend with those of the orbicularis oris. The depressor anguli oris,' fig. 29, t, arises from the external oblique line of the mandible: its fibres ascend and converge to the angle or commissure of the lips, blending with the other insertions at that part.

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The buccinator, fig. 30, b, arises from both upper and lower jaws and the pterygo-maxillary ligament: its fibres line the cheek and converge toward the angle of the mouth, where some decussate, the lower ones going to the upper segment of

30

the orbicularis, the upper ones to the lower segment, while other fibres are continued forward into the corresponding lip. The buccinator acts, in antagonism with the orbicularis, in spirting fluids from the mouth and in playing on wind instruments. In mastication the buccinator presses the food from between the check and gums into the cavity of the mouth. It assists also in deglutition when the mouth is closed, by pressing the food backward. The levator labii superioris alæque nasi' arises from the nasal process of the maxillary, descends obliquely outward and divides, a short strip being attached to

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the cartilage of the ala nasi, the outer and longer strip to the skin of the upper lip near the nose, and becoming blended with the orbicularis and levator labii proprius. The triangularis nasi,' or compressor naris,' figs. 29, and 30, n, arises from the maxillary external to the incisive fossa: its fibres proceed upward and inward, expanding to an aponeurosis continuous, over the bridge of the nose, with that of the opposite muscle. The 'depressor alæ nasi' is a short flat muscle radiating upward from the myrtiform or incisive fossa of the maxillary; it sends upper fibres to the septum and back part of the alæ nasi and lower ones into the orbicularis oris. The orbicularis palpebrarum,' fig. 29, o, surrounds the orbit and eyelids: it arises from the internal angular process of the frontal, from the nasal process of the maxillary, and by a short tendon at the inner angle of the orbit. It rapidly expands to form a broad thin elliptical plane of fibres: the palpebral portion is thin and pale: the orbital portion is thicker and of a reddish colour. The action of the muscle is that of a sphincter, the curved fibres in contraction approaching the centre: but as they are fixed at the inner side the skin to which the muscle is attached is drawn toward the nose, and becomes corrugated into folds which converge toward the inner canthus. The corrugator supercilii, is a small triangular muscle placed at the inner end of the eyebrow, arising from the same end of the superciliary ridge: its fibres pass upward and outward to be inserted into the under surface of the orbicularis palpebrarum. It depresses the eyebrow, and, in conjunction with its fellow, throws the integuments into vertical folds as in the act of frowning. The occipitofrontalis' consists of an anterior and posterior carneous expansion united by a broad' epicranial,' aponeurosis. The anterior muscle, fig. 28, f, consists of two lateral portions, each connected inferiorly with the integument of the corresponding eyebrow, and slightly overlapped by the orbicularis.' The posterior or occipital portion, ib. o, also consists of a pair, attached inferiorly to the upper curved line of the superoccipital, and to the mastoid. The fibres are parallel and nearly vertical. The action of this muscle is most apparent upon the skin of the forehead and the eyebrows: it raises the latter and throws the former into transverse wrinkles.

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§ 202. Locomotion of Mammals.-In the movements of the human frame the three kinds of lever are exemplified. Those of the head upon the atlas are on the principle of the first kind, fig. 31, in which the fulcrum F is between the power P and the resistance When the body is raised on tip-toe by the action of the

W.