Interparietal bone

The Inca leg or the Inca bone (Latin Os INCAE or Os interparietal; . Engl inca bone or incarial bone ) is the skull of a human being ancillary (additional ) bones in the lambdoid suture (lat. suture lamdoidea ), the connection between the parietal ( parietal ) and occiput ( occipital bone ). This surplus represents bone ( bone switch ) an anatomical variation that is not clinically relevant. The radiological diagnosis of skull films can be mentioned as an incidental finding. In many other vertebrates, the os interparietal occurs regularly.

Because of persistent suture mendosa remains a single continuous piece of bone of the occipital exist. The shape of the Inca bone is usually triangular, but can vary significantly and can be rectangular, diamond -shaped or M- shaped. Very rarely the Inca leg can also be two or three divided or more parts included (1 = Os INCAE totum 2 = Os INCAE bipartitum 3 = Os INCAE Tripartitum ), since sometimes more one or more longitudinal seams or an additional transverse seam exists. It can include the skull bone in its entire thickness, or present only on the outside or inside of the skull bone.

The Inca bone was first described in 1851 by ME Rivero and SJ Tschudy of Peruvian skulls of the Incas. Le Double described this bone in 1903 as Os interparietal. Even with fossil Hominini (among Australopithecus and Homo erectus ) and the early Homo sapiens, the Inca bone was found.

Anatomy

The Inca leg has its embryonic origin in the occiput, but is separated from it by an additional suture, as an additional ossification center was established in occiput. The Inca leg is so anatomically the anterior part of the occipital bone is usually the early fixed fuses with the posterior part of the occipital bone. In Peruvian mummies the Inkabei but was found separately. This can be explained as patency of fetal transverse seam in the occipital bone, which leads to the separation of this portion of the rear skull.

The Inca leg is limited from occiput, from the occipital (Latin squama occipitalis ), and both parietal bones. The seam between the Inca bone and occipital bone corresponds to the suture mendosa of the fetus. This cross- seam between the Inca bone and occipital bone lies at the level of the uppermost Linea nuchea and is then referred to as occipital suture transversa - in a way the right and left suture mendosa that are fused in the midline.

In reptiles and many mammals the intermediate parietal bone occurs (Os interparietal ) on a regular basis.

Embryology

In the development phase of the occipital bone (Latin squama occipitalis ) of the occipital bone, a distinction is made ​​between:

• Upper Scale ( produced by intramembranous ossification, a membrane )
• Under Scale ( created by chondral ossification of cartilage)

Between the upper and lower scale runs the suture mendosa. You ossified in the 3rd month of life and then as superior nuchal line (upper Nachenlinie ) visible on the bone.

The upper part of the occipital bone of the occipital bone develops from a membrane, while the rest of the occipital bone from cartilage developed. Within the membrane from the upper portion of the occipital plate should be a single ossification occurs in action. Normally, the upper part of the occipital bone fuses with the original cartilaginous lower part of the occipital bone. If the merger is omitted, the Inca leg forms.

The upper portion of the interparietal bone forms the upper scale of the occipital bone. The interparietal bone is in the development phase of the skull a paired bone deck core, which is originated on the basis of connective tissue, and forming the upper part of the occipital bone. In Nichtverschmelzen the Inca bone is formed.

The occipital bone develops from 5 or 6 ossification.

The small fontanelle in neonates is in the same range as the Inca bone, at the point where the parietal bones with the occipital bone. In some newborns, the fontanelles may be wide open and be covered by additional, free-floating bones. These bones are not important in itself, but can occur together with other, more important anomalies.

Frequency

The Inca leg, which occurs in 20% of ancient Peruvian skull, is a genetic anomaly that was first discovered by the Incas, as they frequently occur in them. Later, it was also found more frequently in Japanese, Koreans and Tibetans.

In the population of America, the Inca leg in Northeast Asia and Australia is more common, rare, however. The populations in Tibet, Nepal, Sikkim and Assam ( Northeast India ) have frequently Inca legs than the neighboring populations. In Europe and in Central and West Asia Inca legs are very rare, more commonly, however, in sub-Saharan Africa. Because of the observed frequency distribution of a causal genetic factor for the Inca leg can not be excluded.

The Inca bone is encountered, depending on the population 3 to 36% of the population.

• London: 8%
• Burma: men 19 %, women 8%
• Mexico: men 36 %, women 28 %

The Inca leg represents an anatomical variety, as well as seam bone, the sacralization of lumbar vertebrae or Steißwirbels or dental anomalies. It is the Inca bone is not a malformation.

Other anatomical abnormalities of the skull, most of which are to be interpreted as setbacks to animal ancestors of man are:

• Patency of the frontal suture in the frontal bone ( Metopismus ) Intermaxillarnaht ( premaxillary ) or Interparietalnaht ( Inca bone )
• Presence of one or more unusually large switching bone (Os epactale )
• Presence of a third pivot knob, a Jugularapophyse, a intermediaries occipital pit, a palate or Hinterhauptwulstes, a lemur extension, an H- or X-shaped arrangement of the Pterions ( the thinnest part of the skull cap ), etc.

From previous ethnologists the Inca leg was listed in the breed classification of people ( racial theories ) as a racial characteristic, as well as the Mongolian fold. More recent studies on the global frequency distribution of the Inca bone refute, however, that the Inca bone is a feature of identification " Inca race". Thus, the interpretation of a mummy discovery in Norway (2007, St. Nikolas Church of Sarpsborg, Østfold Province, message in the Aftenposten, and a message in The Norway Post) is incorrect. There, a 1000 year old mummy was found and " positively identified as the Inca Indians, as the Inca bone is known only by members of the Incas " because of the existing Inca bone.

Causes

Tøgersen in 1951 found in his study that the Inca bone is inherited dominantly and a penetrance of 50 % has. On the other hand, can also contain artificial cranial deformation discussed as the cause ( Ossenberg, 1970; Lahr, 1996), since the deformed brain skulls frequently Inca legs are encountered. The ancient Peruvian skulls were often artificially deformed.