Final answer:
The layer indicated by the arrows in a diagram of a synovial joint is the synovial membrane, responsible for secreting synovial fluid that lubricates and nourishes the joint.
Step-by-step explanation:
Using the generalized diagram of a synovial joint, the layer indicated by the arrows can be identified as the synovial membrane. This membrane lines the inner surface of the articular capsule and plays a critical role in producing synovial fluid. The fluid serves as a lubricant, which reduces friction and nourishes the articular cartilage that covers the articulating surfaces of each bone within the joint.