Page:The American Cyclopædia (1879) Volume XV.djvu/85

 SKELETON 77 FIG. 5. Ethmoid Bone, seen from behind. 1. Central lamella. 2. Cribriform plate. 8. Crista galli. 5, 6, 7. Lateral mass of left side. FIG. 6. Hyoid or Tongue Bone, seen in front. 1. Body. 2, 2. Greater cornua. 8, 8. Lesser cornua. FIG. 7. Palmar Surface of Eight Carpus and Metacarpus. 1. Scaphoid bone. 2. Lunar. 8. Cuneiform. 4. Pisiform. 5 Trapezium. 0. Trapezoid. 7. Magnum. 8. Unciform. a, &, c, d, e. The five metacarpal bones. FIG. 8. Tarsus and Metatarsus, forming Instep. 1. Astragalus. 2. Os calcis. 3. Boat-shaped or scaphoid bone. 4. Cu- boid. 5. Internal cuneiform. 6. Middle cuneiform. 7. External cuneiform, a, &, c, rf, e. The five metatarsal bones. cates with the nasal passage. The lachrymal bones are small oval plates situated at the in- ner angles of the orbits of the eyes. The palate bones are situated at the posterior part of the nasal passages, and enter into the formation of the roof of the mouth or palate and the back part of the floor of the orbits of the eyes. The lower jaw bone consists of a horizontal semicircular portion, having an alveolar process into which the lower teeth are set, and of a perpendicular portion, the ramus, divided into two branches, one of which terminates in the condyle to form the joint, and the other is the coronoid process, into which are inserted the fibres of the temporal muscle and a portion of those of the masseter, the two principal mus- cles of the jaw. The floor of the skull is di- vided into anterior, middle, and posterior f OSSGB, the two fiqst lodging the anterior and middle lobes of the cerebrum, and the posterior fossse lodging the cerebellum. (See BEAIX.) The bones of the trunk are 54 in number, viz. : the 24 bones called vertebrae, constituting, with the sacrum upon which they rest, the spinal column, 24 ribs, 4 pelvic bones, 1 sternum or breast bone, and 1 tongue bone. The two hip bones are naturally classified with the lower extremities, but as they are joined to the sa- crum by immovable sutures, and form with it an important piece of animal mechanism, the pelvis, they are here included in the bones of the trunk. (See PELVIS.) The spinal or ver- tebral column, or backbone, forms the axis of the trunk, supporting it and the skull. All of the vertebra? but one have their principal features in common; i. e., they have a body, a spinous process, a spinal foramen for trans- mitting the spinal cord, and four articular processes, two superior and two inferior for articulating with each other. The spinous pro- cesses which project posteriorly together form the " spine," which marks the course of the spinal column. The uppermost vertebra, called the atlas, has no body, but its place is occupied by a tooth-like process of the bone next below, called the axis, around which the atlas turns. There are 7 cervical, 12 dorsal, and 5 lumbar vertebrae. The seventh cervical is peculiar from having a longer and more prominent apinous process than the others, which may be felt at the base of the neck. Between the bodies of the vertebraa are placed the elastic intervertebral cartilages, which permit flexion of the spinal column and prevent concussion of the spinal cord in walking and leaping. The ribs, 24 in number, are long flat bones of a semicircular form, and have an oblique posi- tion, their posterior extremities being higher than their anterior. The middle part of the curve is also depressed, so that the contrac- tion of the respiratory muscles expands the cavity of the chest. There are 7 true and 5 false ribs on each side, the true ribs articula- ting with the sternum, while the false ribs lap on to each other, except the last two, which are free, and are called floating ribs. The sternum is a kind of breastplate, composed of three pieces, to which the collar bones and the ribs are attached. The tongue bone supports the root of the tongue and gives attachment to muscles for moving it. The upper extremities contain 64 bones, 32 on each side, in six divi- sions : 1, the shoulder ; 2, the arm ; 3, the forearm ; 4, the wrist or carpus ; 5, the palm or metacarpus; 6, the fingers or phalanges. The shoulder contains two bones, the scapula and clavicle. The scapula is a flat triangular bone situated at the upper and back part of the chest on each side. It is traversed on its posterior surface by a spine which terminates in the acromion process, the prominent point of the shoulder. Below the acromion process is the head of the scapula, containing a shallow cup called the glenoid cavity, which receives the head of the arm bone or humerus. The outer extremity of the collar bone or clavicle (Lat. clavis, a key) articulates with the acro- mion process, forming a kind of brace. The scapula is held to the trunk by powerful mus- cles, which allow of sufficient motion to give a variety of positions to the shoulder joint. The arm contains one bone, the humerus, the lower end of which by its expanded articular surface forms with the two bones of the forearm, the radius and ulna, the elbow joint. The wrist or carpus contains 8 bones (see fig. 6), the palm or metacarpus 5, and the fingers or pha- langes 14, the first and second phalanx con- taining 5 each and the third 4. The apparatus of the forearm is a marvel of animal mecha- nism. The upper extremity of the ulna forms with the articular surface of the humerus a firm hinge joint, but the head of the radius forms with it a rotatory joint by which prona- tion and supination of the forearm and hand are effected with grace and facility. The lower extremities contain 60 bones, 30 in each limb, in six divisions : 1, the thigh bone or femur ; 2, the knee pan or patella; 3, the two bones of the leg, the tibia and fibula ; 4, the V bones of the ankle or tarsus ; 5, the 5 bones of the metatarsus ; and 6, the 14 bones of the toes or phalanges. The femur is the longest, largest, and strongest bone in the skeleton. Its upper extremity contains the head, which fits into the socket of the hip bone, and the neck, which joins the shaft of the bone at an angle of near- ly 45, the union being marked by two strong