Variations and abnormalities of the development of the skull bones
Last reviewed: 19.10.2021
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Variants and abnormalities of the development of the skull bones are quite common.
The frontal bone. In about 10% of cases, the frontal bone consists of two parts, a frontal suture (sutura frontalis, s. Sutura metopica) is maintained between them. The size of the frontal sinus is variable, very rarely the sinus is absent.
Sphenoid bone. Non-convergence of the anterior and posterior halves of the body of the sphenoid bone leads to the formation of a narrow, so-called cranial-pharyngeal canal in the center of the Turkish saddle. Oval and awned holes sometimes merge into one common hole; there may be no spinous aperture.
Occipital bone. The upper part of the occipital scales entirely or partially can be separated from the rest of the occipital bone by a transverse suture. As a result, a special bone of triangular shape is distinguished - an intertemporal bone (os interparietale). Assimilation of the atlas is rare. Complete or partial fusion of the occipital condyles with the 1st cervical vertebra. Near the occipital bone, there are often additional bones (joint bones, ossa suturalia). Sometimes the external occipital protrusion reaches considerable dimensions. There is also a third occipital condyle located at the anterior edge of the large (occipital) opening. It joins the front arch of the atlas with an additional joint.
Ethmoid bone. The shape and dimensions of the cells of the latticed bone are very variable. Often there is the highest nasal concha (concha nasdlis suprema).
Parietal bone. Due to the fact that the ossification points do not merge, each parietal bone can consist of the upper and lower halves.
Temporal bone. The jugular cutting of the temporal bone can be divided into two parts by the intercostal process. If there is a similar process in the jugular nape of the occipital bone, a double jugular opening is formed. The styloid process of the temporal bone may be absent, but more often it is long, it can even reach the hyoid bone at the ossification of the shilo-lingual ligament.
Upper jaw. Various numbers and forms of dental alveoli and often unpaired incisors characteristic of mammals are observed. On the lower surface of the bone palate along the middle line, a roller is sometimes formed. There are different in size and shape incisive canal and sinuses of the upper jaw. The most severe malformation of the upper jaw is the cleavage of the hard palate - the "wolf mouth", more precisely the non-growth of the palatine processes of the maxillary bones and horizontal plates of the palatine bones.
Cheekbone. A horizontal seam can split the bone in half. A different number of canals penetrating the bone are also observed.
The nasal bone. The shape and magnitude are individual, sometimes the bone is missing, replacing the frontal process of the upper jaw. Often nasal bones are located asymmetrically or fused and form one common nasal bone.
Lacrimal bone. The size and shape of this bone are fickle. Sometimes the absence of a teardrop is replenished with an enlarged frontal process of the upper jaw or an orbital plate of the latticed bone.
Lower nasal conch. The bone is often different in shape and size, especially its processes.
Opener. Can be curved to the right or left.
Lower jaw. The right and left halves of the body are often asymmetric. The dimensions of the angle between the body of the lower jaw and its branch are individual. There is a doubling of the chin aperture and the opening of the lower jaw, as well as the canal of the lower jaw.
The hyoid bone. The size of the body of the hyoid bone, large and small horns is variable.