For the defense, the purpose of Dr. Di Maio’s testimony was to document the injuries and the path of the bullet to show that they were consistent with Mr. Zimmerman’s account of the struggle. The prosecution contends that Mr. Zimmerman’s injuries were relatively minor, defying his claim that his head had struck concrete again and again.

On Tuesday, the chief prosecutor, Bernie de la Rionda, suggested to Dr. Di Maio that perhaps a tree branch or rolling on pavement could have caused the cuts and lumps to his head.

Yes, he replied, but “you’d have to have a tree branch there and I didn’t see any,” he said.

Dr. Di Maio testified that Mr. Zimmerman suffered at least six identifiable injuries to his face and head. Among them, he said, were two separate swollen spots on his head, along with rows of red spots, that were consistent with the assault that Mr. Zimmerman had described. A nose injury — most likely a broken nose that was pushed back in place, he said — and markings on his forehead were consistent with punches, he added.

The fact that there were only two small cuts to the back of the head does not mean his head did not strike the concrete, Dr. Di Maio said.

Head injuries do not necessarily cause visible bleeding, he said. The bleeding often occurs inside the skull, which is why CT scans are used on people with head injuries.

“Everyone has fallen and hit their head, and you don’t get lacerations,” Dr. Di Maio said. “You can get severe head trauma actually without any marks on the head. Or you can get marks, lacerations and contusions and have head trauma.”

Intracranial bleeding is often the most worrisome wound resulting from head injury. As the brain crashes into the skull, it can cause concussions, impairment and death, he said. Dr. Di Maio said Mr. Zimmerman’s wounds could have caused him to feel stunned. The injuries did not appear to be life-threatening, he said.