Fig 3. - Median Sections through normal and Down's Syndrome Skulls.

MEDIAN SECTIONS THROUGH NORMAL and DOWNS SYNDROME SKULLS

At birth the spheno-basilar synchondrosis is patent and the pre and post sphenoid are unfused. Note that the occiput and sphenoid are in a near straight line and at an angle of about 45^o to the horizontal.

2. In the adult observe the large size of the sphenoid sinus and frontal sinuses and note their influence on the configuration of the skull and face. The cranio-facial angle, measured at the midpoint of the optic chiasmal groove from the lines intersecting from nasion and basion, represents the degree of cranial flexure and normally should have a value of about 130^o.

3. In Downs syndrome the sphenoid sinus is missing and the sphenoid body is hypoplastic. The absence of the frontal sinus results in a straight, infantile forehead. The cranial base is still nearly in a straight line, as in the foetal skull, but the angle to the horizontal is steeper. The anterior cavity of the cranium is shorter, steeper and on a higher plane than normal. There is absence of diploe in the vault bones, resulting in a thin, light skull. Nasion is retracted and the maxilla is hypoplastic.