When a medical witness is called in as an expert he is not a witness of fact. Medical evidence of an expert is evidence of opinion, not of fact.
Where there are alleged eye-witnesses of physical violence which is said to have caused the hurt, the value of medical evidence by prosecution is only corroborative. It proves that the injuries could have been caused in the manner alleged and nothing more. The use which the defence can make of the medical evidence, or any medical evidence which the defence might itself choose to bring, is to prove that the injuries could not possibly have been caused in the manner alleged and thereby discredit the eyewitnesses.
Therefore, you must remember this particular point of view that if you believe the eye-witnesses, then there is no question of having it supported by medical evidence; unless the medical evidence again in its turn goes so far that it completely rules out all possibility that such injuries could take place in the manner alleged by the prosecution and that is a point which you should bear in mind, because if you accept the evidence of the eye-witnesses, no question of further considering the medical evidence arises at all.
The only question in that case when you consider the medical evidence is to test the eye-witnesses’ version as to whether any of the particular injuries shown in the report can be caused in the manner alleged by the prosecution. But if you don’t believe the eye-witnesses, then consideration of the medical evidence in any manner becomes unnecessary