the joints between cranial bones of the skull are called

In the forearm, the wide gap between the shaft portions of the radius and ulna bones are strongly united by an interosseous membrane (seeÂ Figure 9.5 b). The gap between the bones may be narrow, with the bones joined by ligaments, or the gap may be wide and filled in by a broad sheet of connective tissue called anÂ interosseous membrane. SyndesmosisĪÂ syndesmosisÂ (âfastened with a bandâ) is a type of fibrous joint in which two parallel bones are united to each other by fibrous connective tissue. Late in life, the sagittal, coronal, and lambdoid sutures of the skull will begin to ossify and fuse, causing the suture line to gradually disappear.įigureÂ 9.6Â The Newborn SkullÂ The fontanelles of a newbornâs skull are broad areas of fibrous connective tissue that form fibrous joints between the bones of the skull. At the time of birth, the frontal and maxillary bones consist of right and left halves joined together by sutures, which disappear by the eighth year as the halves fuse together to form a single bone. Examples of synostosis fusions between cranial bones are found both early and late in life. This fusion between bones is called aÂ synostosisÂ (âjoined by boneâ). At some sutures, the connective tissue will ossify and be converted into bone, causing the adjacent bones to fuse to each other. When the connective tissue between the adjacent bones is reduced to a narrow layer, these fibrous joints are now called sutures. The fontanelles greatly decrease in width during the first year after birth as the skull bones enlarge. After birth, these expanded regions of connective tissue allow for rapid growth of the skull and enlargement of the brain. During birth, the fontanelles provide flexibility to the skull, allowing the bones to push closer together or to overlap slightly, thus aiding movement of the infantâs head through the birth canal. These broad areas of connective tissue are calledÂ fontanellesÂ ( Figure 9.6). In newborns and infants, the areas of connective tissue between the bones are much wider, especially in those areas on the top and sides of the skull that will become the sagittal, coronal, squamous, and lambdoid sutures. (SeeÂ Figure 9.5 a.) Thus, skull sutures are functionally classified as a synarthrosis, although some sutures may allow for slight movements between the cranial bones. The suture is frequently convoluted, forming a tight union that prevents most movement between the bones. In adults, the skull bones are closely opposed and fibrous connective tissue fills the narrow gap between the bones. The fibrous connective tissue found at a suture (âto bind or sewâ) strongly unites the adjacent skull bones and thus helps to protect the brain and form the face. SutureĪll the bones of the skull, except for the mandible, are joined to each other by a fibrous joint called aÂ suture.

(c) A gomphosis is a specialized fibrous joint that anchors a tooth to its socket in the jaw. (b) An interosseous membrane forms a syndesmosis between the radius and ulna bones of the forearm. (a) Sutures join most bones of the skull. Lastly, a gomphosis is the narrow fibrous joint between the roots of a tooth and the bony socket in the jaw into which the tooth fits.įigureÂ 9.5Â Fibrous JointsÂ Fibrous joints form strong connections between bones. This type of fibrous joint is found between the shaft regions of the long bones in the forearm and in the leg. At a syndesmosis joint, the bones are more widely separated but are held together by a narrow band of fibrous connective tissue called aÂ ligamentÂ or a wide sheet of connective tissue called an interosseous membrane. A suture is the narrow fibrous joint found between most bones of the skull.

The gap between the bones may be narrow or wide.

Give an example of each type of fibrous jointĪt a fibrous joint, the adjacent bones are directly connected to each other by fibrous connective tissue, and thus the bones do not have a joint cavity between them ( Figure 9.5).

Distinguish between a suture, syndesmosis, and gomphosis.

Describe the structural features of fibrous joints.

By the end of this section, you will be able to:

The joints between cranial bones of the skull are called