Experts said battered boxers suffer the same kind of head injuries four-year-old John Smith received.

During the trial, Professor Ian Hill, a pathologist, clenched a fist to demonstrate an uppercut punch as the most likely way the boy's upper lip was hit, splitting the frenulum, the web of skin that joins the lip to the gum.

Paediatrician Professor Jo Sibert said the injuries John sustained to his head were like those seen on "unfortunate boxers". The blows were delivered with force.

He said a small cut where his penis joined his body, seen four months before his death, suggested sexual abuse.

A black eye and two line bruises underneath, again seen earlier, suggested a heavy slap with the hand.

A bald patch on the boy's head could have been caused when he was being held as he was abused.

Prof Sibert said: "It would have been extremely painful."

Adult bite marks were also indicative of abuse and would have caused trauma.

Prof Sibert could not rule out the possibility of self-harm but said such extreme injuries were outside his experience.

Dr Ian Kenny, of the Royal Alexandra Children's Hospital, Brighton, said John's fatal head injury was consistent with him being shaken rapidly and thrown against a surface.

Neighbours said they heard repeated banging noises "like a basket ball" on the morning John was found unconscious.

Staff at the Royal Sussex County Hospital, Brighton, were shocked when they first saw the extent of the boy's injuries.

The dummy shows 54 injuries, mostly bruises, on John's head, including his face, jaw, cheek, eye lids, shoulder, chest, arms, wrist, thigh, legs, buttocks and back.

A few were probably caused by John himself at play and some were the result of medical treatment as doctors infused drugs and inserted life-support equipment to try to save him.

The vast majority were non-accidental, the court heard. Marks on the dummy show the bald patch where hair had been torn out while others were identified by experts as adult bite marks.

None of the three dental experts who testified could be definite but two said they were most likely from Simon McWilliam.