center for the shaft (seventh fetal week); one for the base (third year), united by the twentieth year. The second metatarsal, the longest, articulates posteriorly with the middle cuneiform, internally with the internal cuneiform, externally with the external cuneiform and third metatarsal, four bones in all developed by one center (seventh fetal week) for the shaft, one for the head (third year), united at twenty years. The third metatarsal has a facet on the base for the external cuneiform, two on its inner side and one on its outer for the contiguous metatarsal: developed like the second. The fourth metatarsal articulates behind with the cuboid, has a facet on the inner side divided into an anterior portion for the third metatarsal, a posterior for the external cuneiform, and externally one facet for the fifth metatarsal, under which is a deep groove: developed like the second. The fifth metatarsal has a triangular oblique surface for the cuboid, continuous internally with one for the fourth metatarsal; externally a tubercular eminence: developed like the 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 centers appear from the second to the fourth month, and the epiphyses appear at the bases in the fourth to the eighth year. THE ARTICULATIONS. How are the articulations classed? In three divisions: 1. Synarthrosis, immovable, as most of the cranial articulations; 2. Hemiarthrosis, yielding (limited motion), as that between the vertebral bodies, or at the pubic symphysis; 3. Diarthrosis, freely movable. Into what classes are the synarthroses divided? 1. Synchondrosis, union by cartilage, as sacro-iliac joint; 2. Syndesmosis, union by ligament, as sutures; 3. Synostosis, union by bone, as spheno-occipital. Sutures are true and false. 1. Sutura vera, including three sub-classes-S. dentata, tooth-like, as the interparietal suture; S. serrata, like saw teeth, as the interfrontal; S. limbosa, when bevelled in addition to dentation, as the fronto-parietal. The S. notha (false suture) includes 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. Schindylesis, where a thin edge is received into a cleft or groove, as the vomer between the superior maxillary and palate 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 in tarsus and carpus ; enarthroses, ball-and-socket joint-hip- or shoulder-joints; ginglymus, hingejoint elbow-joint; trochoides, or lateral ginglymus, a pivot turning within a ring, as the superior and inferior radio-ulnar and central atlanto-axial; condyloid where surfaces are elliptical, as radio-carpal (wrist); reciprocal reception, or saddleshaped surfaces, as first carpo-metacarpal (base of thumb). Motions. Flexion, extension, adduction, abduction, circumduction (a combination in succession of the four), rotation, and gliding. What structures are essential to the formation of each of the three classes of articulations? 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 are sometimes composed of yellow elastic tissue, as the ligamenta subflava or ligamentum nuchæ); 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 interarticular, 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 the denser articular lamella; it contains neither Haversian canals nor canaliculi, but 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. The Articulations of the Trunk. Describe the vertebral articulations. Formed by the contiguous surfaces of the bodies, laminæ, articular, spinous, and transverse processes; their ligaments are: An intervertebral connecting fibro-cartilage, or disk, between the bodies of all true vertebræ, except the atlas and axis. An anterior common ligaments passing medianly over the fronts of the vertebral bodies, most firmly attached to their margins. A posterior common ligament, similarly disposed behind the bodies. Short or lateral vertebral ligaments, fibers running at most over three vertebræ, firmly uniting the bodies where the anterior and the posterior common ligaments are deficient. Ligamenta subflava, of yellow elastic tissue, connecting the laminæ from an internal surface above to an upper edge below. Capsular, enclosing the articular processes, and lined with synovial membrane. Supra- and interspinous, the former connecting the tips, the latter being interposed between the spinous processes. Intertransverse, connecting transverse processes; nerves, spinal in each region; arteries, vertebral, pharyngeal, and ascending cervical arteries in the neck, intercostal arteries in the thoracic region, and lumbar arteries in the loin. Describe the occipito-atlantal articulation. A pair of ginglymo-arthrodial joints formed by the con |