It is described a surgical instrument such as a speculum comprising longitudinally extending cups-shaped pivotably mounted blades manufactured from a moldable material, such as plastic or metal. Each blade has an inwardly curved circumferential edge with an edge face which is provided with a parting line resulting from molding the blades. Negative effects such as possible injuries associated with parting lines or steps can be mitigated by inwardly relocating these lines on an edge face of the inwardly curved circumferential edge.