

COSTOVERTEBRAL ARTICULATIONS 299 



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 move- 

 ment 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 for- 

 ward 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. 





V. Costovertebral Articulations (Articulationes Costovertebrales). 



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 vertebrae, 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 vertebrae 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 Radiate. The Interarticular. 



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 vertebras. 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 costce radiatum; anterior costoverte- 

 bral or stellate ligament} . The radiate ligament connects the anterior part of the 

 head of each rib with the side of the bodies of two vertebrae, and the interverte- 

 bral 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 sur- 

 face. The superior fasciculus ascends and is connected with the body of the verte- 

 bra 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 interver- 

 tebral 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 synovia! 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 arrange- 



