The more important malformations of bone are connected with general malformations, and have been considered in an earlier part. We have defects of the skull in anencephalus, and of the vertebrae in spina bifida.

Besides these, we have congenital reduplication of bones, such as of the vertebrae, the ribs, the fingers, and toes. Supernumerary vertebras are met with in any of the regions of the column. Supernumerary ribs may be cervical or lumbar. In Supernumerary fingers and toes the bones may be absent, or may be represented only by cartilage.

Certain Malformations of the skull have been ascribed to premature coalescence of the bones at the base, or of the sutures of the cranium, a condition designated Synostosis. The basilar parts of the occipital and sphenoid bones are formed from cartilage. The basilar part of the sphenoid is originally in two parts, presphenoid and postsphenoid, which unite before birth. The sphenoid and occipital bones are separated by cartilage up till the twentieth year, and as this cartilage has the characters of ossifying cartilage, on it the growth in length of the base of the skull depends. A premature synostosis of these two bones will check growth and lead to a Shortening of the base of the skull. To this is ascribed the existence of abnormal retraction of the nose.

The bones of the calvarium grow at their margins, or, in other words, at the sutures. A premature coalescence of the bones or Closure of the sutures will stop this growth. According to the sutures affected the result varies. If all the sutures close there will be a general smallness of the head, a Microcephalus. If there be a premature synostosis of the coronal and lambdoidal sutures, the growth in length is checked, and, as a compensatory growth in breadth occurs, the head is abnormally wide and flat on the vertex, conditions designated by the terms Brachycephalus and Platycephalus. When the sagittal suture is affected, growth in breadth is interfered with and an abnormally long cranium is produced, a Scaphocephalus.

There seems no doubt that microcephalus arising in this way may lead to arrest of the growth of the brain, some cases of idiocy being thus explained. On the other hand smallness of the brain will be associated with smallness of the skull, but this will not be associated with premature synostosis.

A similar Synostosis of the sacroiliac articulation may lead to permanent malformation of the pelvis. If the synostosis occur on one side the sacrum is defective in its lateral mass and the ilium is also imperfectly expanded. These parts being shortened, the ilium has a straighter course from sacrum to symphysis, and the pubic bone of the affected side joins the opposite one at an angle. The pelvis is thus narrowed on the one side. If the synostosis is on both sides, then both iliac bones have a shorter and straighter course, and the pelvis has a more quadrilateral form than normal, and is narrowed transversely.

Literature

Vikchow, Ges. Abhandl. (with classification of forms of skulls), 1856, p. 901; Entwickel. des Schadelgrundes, 1857; Wiirzburger Verhandl., vii., 1857; Virch. Arch., v., xiii., and xciv.; Litzmann (Synostosis in pelvis), Arch. f. Gyn., xxv., 1884.