3. Os enboideum, (Os rubiforme, Fr. le cu boide, Germ. dos lirmfelbein.)—This hone forms the external one of the second row of tarsal bones ; it is situated between the os calcis behind and the fourth and fifth meta tarsal bones in front ; in point of size it ranks next to the astragalus. Six surfaces may be described upon it. a. The superior or dorsal surface, forming an inclined plane, directed downwards and outwards; it is rough for liga mentous insertion. b. The external surface, more properly an edge, very limited in extent, chiefly occupied by the commencement of the groove for the peroncus longus muscle. c. The inferior or plantar surface, which in front pre sents a deep groove directed obliquely forwards and inwards, parallel to the anterior edge, and destined to lodge the tendon of the peroneus longus. The posterior edge of this groove is very prominent, and with the remainder of this surface, which is rough, affords insertion to the calcaneo-cuboid ligament. d. The internal surface has at its upper and posterior part a triangular plane articular facet for articulation with the external cuneiform bone, and some times a smaller one for articulation with the navicular; the rest of this surface is irregular and rough for ligamentous insertion. e. The anterior or metatarsal surface is wholly arti cular, and is divided by a vertical line into two facets, an outer one triangular and plane for the fifth, and an inner one quadrilateral and very slightly concave for the fourth metatarsal bone. The external of these facets is inclined obliquely outwards and backwards. J. The posterior surface is oval, with its long axis directed downwards and outwards ; it is wholly articular and adapted to the anterior surface of the os calcis.
4. Os sraphoideum (from cmcapn, navis, os naviculare, Fr. le scaphoide, Germ.dasKahnbein, oder Schitiormige Knochen,) forms the posterior and internal bone of the second tarsal row, and is placed between the three cuneiform bones in front and the astragalus behind. It is oval in shape, with its long axis directed obliquely downwards and inwards; the small end of the oval is situated internally and inferiorly, and presents a distinct prominence or process (tuber ossis navicularis), which gives insertion to some fibres of the tendon of the tibialis posticus.
Four surfaces may be described upon this bone. a. The superior or dorsal surface, of great extent, convex, very rough for the inser tion of ligaments, and perforated by foramina. b. The inferior surface, irregularly concave, and very rough, also affording insertion to ligaments. c. The posterior surface, entirely articular, oval and concave, adapted to the head of the astragalus, although considerably less in extent than it. This constitutes what is called the glenoid cavity. d. The anterior sur face, also articular and convex, divided by two lines which converge from above downwards, into three triangular surfaces for articulation with the three cuneiform bones.
5. Ossa runeiformia (Fr. les os euneiformes, Germ. die Keillormigen Knochen.) These bones are interposed between the navicular bone behind and the three internal metatarsal hones in front ; they are arranged in the form of an arch, of which the middle cuneiform is the central or key-bone. Each is very distinctly
wedge-shaped; the two outer ones have the acute edge directed downwards, but the inter nal one has it directed upwards.
The internal cuneiform bone is at once dis tinguishable from the others by its great size. By means of an oval concave articular surface, whose long axis is vertical, it is articulated with the anterior and internal part of the navi cular bone, and in front a large and irregular, slightly concave articular facet adapts it to the posteriur extremity of the metatarsal bone of the great toe. Its inner surface is convex and rough for ligamentous insertion ; on it, towards its anterior part, we observe an impression, sometimes an eminence, for the insertion of the tibialis anticus tendon ; and its plantar surface, the base of the wedge, is thick and prominent, and affords insertion to ligamentous fibres as well as to those of the tibialis postieus tendon. The external surface is articulated in front with the second metatarsal bone, and behind with the middle cuneiform, by means of an oblong articular facet, which extends along the upper part of this surface from before backwards parallel to the acute edge. The remainder of the external surface is rough for ligamentous insertion, excepting a small por tion about the sixth of an inch broad, which, extending along the posterior edge, is articular and continuous with the posterior surface of the bone.
The middle or second cuneiform bone is the smallest of the three ; its base is uppermost, rough and convex ; its posterior surface is tri angular with the base superior; it is articular and adapted to the middle facet on the anterior surface of the navicular; its anterior surface is also triangular and articulated with the second metatarsal bone ; its inner surface is articular along its upper and posterior edges, and rough in the remainder of its extent; this surface is in contact with the inner cuneiform. The outer surface is articular along half of its upper edge and the whole of its posterior, but rough in the remainder, and by means of the articular portions is connected with the external cunei form bone.
The external or third cuneiform bone is second in point of size ; it is bounded on the outside by the cuboid, behind by the navicular, on the inside by the middle cuneiform, and in front by the third metatarsal bone. Its pos terior and anterior surfaces are both plane and articular, the one for the navicular, the other for the third metatarsal bone. The base of the wedge is situated on the dorsal surface of the foot, and is rough. The internal surface presents at its posterior edge a facet for arti culation with the middle cuneiform, and in front another for the second metatarsal ; the re mainder is non-articular. The external surface presents, towards its upper and posterior angle, a plane triangular facet, which is adapted to a similar one on the inner surface of the cuboid, but in the rest of its extent it is rough and non articular.