Section 113J. Any company issuing or executing a motor vehicle liability policy or bond, both as defined in section thirty-four A of chapter ninety, which requests and makes a medical examination of a person injured in an accident involving a motor vehicle, shall, upon request of the injured party or his attorney, furnish said party or attorney with copies of reports of all medical examinations made by said insurer; provided, that such injured party shall, upon request of said insurer, furnish it with copies of reports of all medical examinations and treatment made by his attending physician or physicians.