The right and left heads of the mandibular condyles articulate in the temporomandibular or glenoid fossae. At birth, the heads of the condyles are round and covered with a thick layer of cartilage. The cartilage front is uneven with spikes of cartilage projecting into the underlying marrow space. Bone forms around these spikes so the head of the condyle is porous (Fig. 13-2, A). During development, the condyle grows in a lateral direction, changing into an ovoid shape by maturity, which is attained at age 25 years (Fig. 13-2, B). The oval condyle consists of a smooth, bony surface, which is covered with a layer of fibrous connective tissue in the adult. The cartilage serves as a growth site in the condyle.

New cartilage cells arise from near the surface of the perichondrium, which covers the condyle. The cartilage cells grow and divide, and the cells deeper in the cartilage die as the cartilage that surrounds these cells calcifies (Fig. 13-3, A). The calcified cartilage is then replaced by bone from the underlying ramus (Fig. 13-3, B). This process continues during development with a gradual thinning of the cartilage layer, and at maturity the cartilage has been replaced by bone (Fig. 13-3, C).

The heads of the condyles and the heads of the long bones differ in that long bones form secondary ossification centers (Fig. 13-4). Secondary ossification centers produce cartilage–bone junctions termed epiphyseal lines, where the lengthening of long bone occurs. No epiphyseal line is formed in the condyles. The heads of the condyles, however, accomplish growth much like that of long bones. Differentiation of new cartilage cells first appears, then cartilage matrix around these cells develops, which is then replaced by bone. Another difference in long bones is that the cartilage cells are organized in long rows as they approach the bony junction, whereas in the condyles the chondroblasts are scattered. The chondroblasts go through similar changes of cell enlargement, cartilage matrix calcification, and bony replacement (see Fig. 13-4). This ability to modify the shape of the condyles through cartilage–bone remodeling allows adaptation to functional stress.

The fossa is composed of an anterior part in the form of an eminence and a posterior part, a depression or cavity on the inferior part of the temporal bone. This fossa is located at the posterior medial aspect of the zygomatic arch (Fig. 13-5). The anterior wall of the fossa is smooth and forms a tubercle in which the condyles slide during articulation. On the posterior wall of the fossa is the petrotympanic fissure.

The contents of the fissure include communications of cranial nerves VII and IX to the infratemporal fossa. A branch of cranial nerve VII, the chorda tympani, runs through the fissure to join with the lingual nerve providing special sensory (taste) innervation to the tongue. The tympanic nerve branches off of cranial nerve IX to pass through the fissure as the lesser petrosal nerve, which passes through the foramen ovale and joins V₃ of the trigeminal nerve, synapses in the otic ganglion, and provides parasympathetic innervation to the parotid gland.

This is the junction of the temporal and parietal bones. Some authors report that the origin of elastic fibers, which insert into the posterior part of the disk, is on the posterior wall of this fissure. These elastic fibers may function in retrac/>