Henry Gray (18251861). Anatomy of the Human Body. 1918.
the movement is confined to the lower of the two joints. On the other hand, when the mouth is opened more widely, both joints are concerned in the movement; in the lower joint the movement is of a hinge-like character, the condyle moving around a transverse axis on the disk, while in the upper joint the movement is of a gliding character, the disk, together with the condyle, gliding forward on to the articular tubercle, around an axis which passes through the mandibular foramina. These two movements take place simultaneously, the condyle and disk move forward on the eminence, and at the same time the condyle revolves on the disk. In shutting the mouth the reverse action takes place; the disk glides back, carrying the condyle with it, and this at the same time moves back to its former position. When the mandible is carried horizontally forward, as in protruding the lower incisor teeth in front of the upper, the movement takes place principally in the upper joint, the disk and the condyle gliding forward on the mandibular fossa and articular tubercle. The grinding or chewing movement is produced by one condyle, with its disk, gliding alternately forward and backward, while the other condyle moves simultaneously in the opposite direction; at the same time the condyle undergoes a vertical rotation on the disk. One condyle advances and rotates, the other condyle recedes and rotates, in alternate succession.
The mandible is depressed by its own weight, assisted by the Platysma, the Digastricus, the Mylohyoideus, and the Geniohyoideus. It is elevated by the Masseter, Pterygoideus internus, and the anterior part of the Temporalis. It is drawn forward by the simultaneous action of the Pterygoidei internus and externus, the superficial fibers of the Masseter and the anterior fibers of the Temporalis; and backward by the deep fibers of the Masseter and the posterior fibers of the Temporalis. The grinding movement is caused by the alternate action of the Pterygoidei of either side.
5e. Costovertebral Articulations
The articulations of the ribs with the vertebral column may be divided into two sets, one connecting the heads of the ribs with the bodies of the vertebræ, another uniting the necks and tubercles of the ribs with the transverse processes.
1. Articulations of the Heads of the Ribs (articulationes capitulorum; costocentral articulations) (Fig. 312).These constitute a series of gliding or arthrodial joints, and are formed by the articulation of the heads of the typical ribs with the facets on the contiguous margins of the bodies of the thoracic vertebræ and with the intervertebral fibrocartilages between them; the first, tenth, eleventh, and twelfth ribs each articulate with a single vertebra. The ligaments of the joints are:
The Articular Capsule.
The Articular Capsule (capsula articularis; capsular ligament).The articular capsule surrounds the joint, being composed of short, strong fibers, connecting the head of the rib with the circumference of the articular cavity formed by the intervertebral fibrocartilage and the adjacent vertebræ. It is most distinct at the upper and lower parts of the articulation; some of its upper fibers pass through the intervertebral foramen to the back of the intervertebral fibrocartilage, while its posterior fibers are continuous with the ligament of the neck of the rib.
The Radiate Ligament (ligamentum capituli costæ radiatum; anterior costovertebral or stellate ligament).The radiate ligament connects the anterior part of the head of each rib with the side of the bodies of two vertebræ, and the intervertebral fibrocartilage between them. It consists of three flat fasciculi, which are attached to the anterior part of the head of the rib, just beyond the articular surface. The superior fasciculus ascends and is connected with the body of the vertebra above; the inferior one descends to the body of the vertebra below; the middle one, the smallest and least distinct, is horizontal and is attached to the intervertebral fibrocartilage. The radiate ligament is in relation, in front, with the thoracic ganglia of the sympathetic trunk, the pleura, and, on the right side, with the azygos vein; behind, with the interarticular ligament and synovial membranes.
In the case of the first rib, this ligament is not divided into three fasciculi, but its fibers are attached to the body of the last cervical vertebra, as well as to that of the first thoracic. In the articulations of the heads of the tenth, eleventh, and twelfth ribs, each of which articulates with a single vertebra, the triradiate arrangement