Accessory Bones of the Skull
Accessory bones of the skull go by many names including Wormian bones, intrasutural bones or sutural bones. Accessory bones of the skull are formed from additional and separate centres of ossification of the cranium, located near or in the cranial sutures that lead to extra isolated bone segments in the cranium. These small accessory bones tend to vary in size and also tend to be irregular in shape.
Accessory bones of the skull are found in various areas, usually arising in fontanelles and/or adjacent or along the sutures of the skull. The most common location that these accessory bones are found is at the lambdoid and lambdoid (posterior) fontanelle, with some arising at the masto-occipital suture. Sometimes a large isolated interparietal bone is found at lambda, called the Inca bone or Goethe’s ossicle.
The second most common location is at the coronal suture of the skull with the remaining locations at any other sutures and fontanelles. A single or a number of pterion ossicles may be found between the sphenoid angle of the parietal bone and the greater wing of the sphenoid bone. Pterion ossicle(s), again, vary in sizes but are usually symmetrical in shape.