Appellant was convicted of possessing a deadly weapon while in confinement of a penal institution. OCGA 42-5-63 (Code Ann. 77-361). Appellant bases his appeal solely on the general grounds.

At trial, the evidence revealed that Captain William B. Flurry, an employee of the Georgia State Prison at Reidsville, was walking the grounds of the prison when he observed appellant doing something with the front of his shirt and pants. Captain Flurry conducted a pat-down search and found a crude knife about 10 inches long on appellant's person. Appellant claims that he was nowhere near the area where the search allegedly took place.

"The credibility of a witness is a matter to be determined by the jury . . ." OCGA 24-9-80 (Code Ann. 38-1805). We believe that there was sufficient evidence from which a rational trier of fact could find appellant guilty as charged beyond a reasonable doubt. Jackson v. Virginia, 443 U. S. 307 (99 SC 2781, 61 LE2d 560).