None of the soft tissues, such as skin, muscles, or brain matter, were preserved in the Starchild Skull. However reserchers are still able to tell us a lot about the brain the Skull once held. In 2012, Medical Modeling of Colorado, USA, used detailed scans of the Starchild to create an exact 3D replica of the inside of the Skull, showing in moderate detail what it's brain would have looked like. While this technique can never produce an exact replica of the living brain, the same technology was used to create brain casts of both the Starchild and a normal human, so it is possible to accurately compare the two.
The Starchild has the same two lobes as a normal human brain, however the shape is quite different, and the brain itself is significantly larger. A human child has a brain about 1200 cc in size, while an adult is about 1400 cc. The Starchild's brain was about 1600 cc, significantly larger than a normal human.
X-Rays show veinous imprints on the inside of the Skull, the dents left in the bone where veins once existed. This shows that the brain filled the entire skull cavity, and is important because this helped experts to rule out Hydrocephaly as a cause for the unusual properties of the Skull. Read more about Hydrocephaly HERE.