The scaphoid, situated internally, is concave behind for the head of the astragalus; is convex in front with three facets for the three cuneiform bones; externally is a facet for the cuboid; and internally, below, is the tuberosity for part of the posterior tibial tendon; it is developed from one centre (fourth year).

The internal cuneiform, the largest, is placed at the inner side of the foot, has its base downward, upon which is the tuberosity for part of the tendon of the posterior tibial muscle; in front is a kidney-shaped facet for first metatarsal; externally are two facets for the second metatarsal in front, the middle cuneiform behind; posteriorly a facet for the scaphoid; it is developed by one centre (third year).

The middle cuneiform, the smallest, has its base upward, a triangular facet in front for second metatarsal, another behind for the scaphoid; along the posterior and superior borders of the inner face a facet for the internal cuneiform; and externally a smooth facet for the external cuneiform; it is developed by one centre (fourth year).

FIG. 41.

The external cuneiform is intermediate in size with base upward, has an anterior triangular facet for third metatarsal; another posterior for the scaphoid; two upon internal surface for second metatarsal and middle cuneiform; and two upon outer surface for fourth metatarsal and for cuboid: it is developed by one centre (first year).

Describe the metatarsal bones.

These five long bones have prismoid shafts, anteriorly a head for articulation with the phalanges, posteriorly a base articulating with the tarsus and one another.

The first metatarsal is shorter, much stouter, and articulates only with the internal cuneiform: developed by one centre for shaft (seventh foetal week); one for base (fifth year), united by the twentieth year.

The second metatarsal, the longest, articulates posteriorly with the middle cuneiform, and laterally with the other cuneiforms, presenting, therefore, three facets on base; developed by one centre (seventh fœtal week) for shaft, one for head (third year), united at twenty years.

The third metatarsal has a facet on base for external cuneiform, two on its inner side and one on its outer for the contiguous metatarsal; developed like second.

The fourth metatarsal articulates behind with cuboid, has a facet on inner side divided into anterior portion for third metatarsal, a posterior for external cuneiform, and externally one facet for fifth metatarsal: developed like second.

The fifth metatarsal has a triangular oblique surface for the cuboid, continuous internally with one for fourth metatarsal; externally a tubercular eminence; developed like second.

Describe the phalanges.

They resemble closely those of the hand, except that they are strongly compressed from side to side, instead of from before backward: ossification also, similar but later. Thus, the shaft centres appear from two to four months, except distal at seventh foetal week.

THE ARTICULATIONS.

How are the articulations classed ?

In three divisions;(1, Synarthroses, immovable, as most of cranial articulations; 2. Amphiarthroses, including ynchondroses, or symphyses, yielding (limited motion), as those between the vertebral bodies, the pubic and sacro-iliac symphyses. Diarthroses, freely movable.

Into what classes are the synarthroses divided?

1. Sutura vera, consisting of interlocking serrations, including three sub-classes of S. dentata, when the bony projections are tooth-like, as the inter-parietal suture; S. serrata, when like a fine saw, as the inter-frontal; S. limbosa, when the edges are bevelled in addition to dentation, as the fronto-parietal. The Sutura notha (false

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Cartilage.

2.

sutures) include S. squamosa, formed by two overlapping bevelled edges, as the squamo-parietal suture; and the S. harmonia, mere apposition of roughened surfaces, as the two superior maxillary bones.

2. Schindelysis, where a thin edge is received into a cleft or fissure, as the vomer between the superior maxillary bones.

3. Gomphosis, the insertion of a conical process into a socket, as teeth in their alveoli (not really a bony articulation, as teeth are not bones).

How are diarthroses classed?

As arthrodia, gliding joints—the articular processes of the vertebræ; enarthroses, ball-and-socket joint-hip- or shoulder-joints: ginglymus, hinge-joint-elbow-joint; diarthrosis rotatoria, or lateral ginglymus, a pivot turning within a ring, or a ring on a pivot, as the superior radio-ulnar and atlo-odontoid. (Tchivides (likepled by ddle Recipica recept - thumb) (modif it What varieties of motion do joints enjoy?"

Flexion, extension, adduction, abduction, circumduction (a combination in succession of the four preceding), rotation, and gliding.

What structures are essential to the formation of each of the three classes of articulations?

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For synarthroses, two or more bones, an interposed layer of fibrous tissue (sutural ligament) or, perhaps, cartilage (base of the skull); symphyses, an interposed bond of fibro-cartilage, with strong bands of white fibrous tissue, i. e., ligaments (ligaments it. are sometimes composed of yellow elastic tissue, as the ligamenta subflava or ligamentum nucha), diarthroses, two or more cartilaginous-coated surfaces (reducing friction), sometimes interarticular fibro-cartilages to deepen joint surfaces, as those of the knee- and temporo-maxillary joints, a complete fibrous capsule, and often additional ligamentous bands, some inter-articular, i. e., within the joint cavity, and a synovial (serous) membrane lining the interior of the capsule, but not extending upon the cartilages; a similar membrane also forms sacs (bursæ) outside the joints, with which they often communicate, serving to reduce friction of the tendons, ligaments, etc.; the layer of bone beneath the articular

cartilage is denser, contains neither Haversian canals nor canaliculi, and has larger lacunæ.

What is the rule as regards the nerve supply of joints?

The interior of the joint, the muscles moving it, and the skin over their insertions, are supplied by the same trunk or trunks of nerves (this explains the reflex contractions of diseased joints).

Describe the vertebral articulations.

Formed by the contiguous surfaces of the vertebral bodies and articular processes, their ligaments are as follows:

An intervertebral connecting fibro cartilage, between the bodies of all true vertebræ, except the atlas and axis.

An anterior common ligament3 passing medianally over the fronts of the vertebral bodies, most firmly attached to their margins. A posterior common ligament, similarly disposed behind.

Short intervertebral ligaments, fibres running at most over three vertebræ, firmly uniting the bodies where the anterior and posterior common ligaments are deficient.

Ligamenta subflava, of yellow elastic tissue, connecting the laminæ.

Supra- and inter-spinous, the former connecting the tips, the latter the remainder of the spinous processes.

Capsular, enclosing the articular processes, and lined with synovial membrane.

Inter-transverse, connecting transverse processes; nerves, spinal in each region; arteries, vertebral and ascending cervical arteries in neck, intercostals in dorsal region, lumbars in loin.

Describe the occipito-atloid articulation.

It is a ginglymo arthrodial joint formed by the condyles of the occipital bone and the superior articulating processes of the atlas. Its ligaments are,

An anterior occipito atlantal2 (Fig. 42), extending from the anterior margin of the foramen magnum to the anterior arch of the atlas, about one inch broad, blending on either side with the capsular ligaments.

A posterior occipito-atlantal, much broader, from the posterior margin of the foramen magnum between the condyles, to the pos

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1.

1.

3.

3.

tero-superior border of the posterior arch of the atlas, and is incomplete on each side for the ingress of the vertebral artery, and egress of the suboccipital nerve.

Two capsular ligaments, lined with synovial membrane, surrounding the articular surfaces.

Two lateral (or anterior oblique), passing upward and inward from the transverse process beyond the vertebral foramen to the inner edge of the jugular foramen;

nerve, suboccipital; arteries, from vertebral.

Describe the atlo-axoidean points.

The lateral joints are arthrodia, that between the atlas and odontoid process a double diarthrosis rotatoria. The ligaments of the lateral joints and arches are,

The anterior atlanto-axoidean*,

FIG. 42.

membranous, passing between lower front border of atlas to front of the axis.

The posterior atlanto-axoidean, stretching between the posteroinferior edge of the ring of the atlas to the superior edge of the arch of the axis behind; it is pierced on each side by the second spinal nerve.

The anterior 1-3 and posterior common ligaments are continued over the median portions of the above to the occiput.

Two capsulars, synovial-lined, surrounding the articulating processes.

The ligaments of the central atlanto-axoidean joints are:

The transverse (Fig. 43), extending between the tubercles on the inner surface of each lateral mass of the atlas; it holds the odontoid process in place, and between the two is a synovial membrane surrounded by, a capsule, the odonto-transverse joint; between the odontoid process and the posterior surface of the anterior arch of the atlas, is the atlo-odontoid articulation, surrounded by a capsule lined with synovial membrane; passing upward and downward, are two strong vertical bands, attached above to the cranial surface