Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Bone Articulations
Articulations of the Bones of the Skull

The BONES OF THE Skull are interconnected primarily by continuous joints. The only interrupted joint is the temporomandibular joint.

In adults, the bones of the cranial vault are connected by sutures. According to their shape, sutures are classified into serrate, squamous, and plane sutures. Serrate sutures are located between the parietal bones (sagittal suture); between the parietal and frontal bones (coronal suture); and between the parietal and occipital bones (lambdoid suture). The squamous suture connects the squamous part of the Temporal bone with the Parietal bone and the greater wing of the Sphenoid bone. The bones of the facial Skeleton are connected by means of plane (harmonic) sutures. The names of the sutures are derived from the names of the bones they connect, for example: frontozygomatic, zygomaticomaxillary, etc.

In the SKULL OF A fetus, newborn, and a child During the first two years of life, fontanelles are present In addition to plane sutures (see Section 4.3).

Cartilaginous joints—synchondroses—are characteristic of the cranial base bones in children. With age, the Cartilage is gradually replaced by Bone tissue.

The temporomandibular joint, articulatio temporomandibularis, is a condylar, combined joint. It is formed by the HEAD of the Mandible, the mandibular fossa, and the articular tubercle of the temporal bone (Fig. 5.4). The articular surfaces are lined with fibrocartilage.

A distinctive feature of the temporomandibular joint is the presence of an articular disc, which ensures the congruence of the articular surfaces. The anterior section of the Joint Capsule is thinner. The capsule is fused with the articular disc across its entire surface, As a result of which the joint cavity is divided into upper and lower compartments. On the lateral side, the joint is reinforced by the lateral ligament.

The following types of movements are possible in the temporomandibular joint: 1) around the frontal axis—elevation and depression of the mandible, protrusion of the mandible forward and its return backward with the simultaneous displacement of this axis; 2) around the vertical axis—rotation.

During depression of the mandible, the head slides forward and, upon maximum Mouth opening, moves onto the articular tubercle. Excessive depression of the mandible may lead to its dislocation—displacement anterior to the articular tubercle. When the mandible is protruded, the condylar processes along with the articular discs slide forward and move onto the tubercles in both joints. During the Rotation of the mandible, the movements in the right and left joints differ. In this case, in one joint (toward which the movement is directed), rotation occurs within the fossa, while in the other joint, the head along with its disc moves onto the tubercle, performing a circular motion.

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Fig. 5.4. Temporomandibular joint:

1 — joint capsule; 2 — mandibular fossa; 3 — articular disc; 4 — articular tubercle; 5 — mandible; 6 — stylomandibular ligament; 7 — styloid process; 8 — head of the mandible