Final answer:
An aponeurosis is a broad, flat sheet of connective tissue differing from the rope-like structure of a tendon, which is a cord of collagen fibers aligned in parallel. Tendons focus on transmitting muscle force to bones in a specific, narrow area, whereas aponeuroses distribute muscle tension across a wider surface.
Step-by-step explanation:
An aponeurosis and a tendon are both structures that connect muscle to bone, but they have different structural features. An aponeurosis is a broad, flat sheet of connective tissue that attaches muscles to the parts they move. In contrast, a tendon is a more rope-like, cord of dense regular connective tissue that connects muscles to bones. The key structural difference is that tendons are formed by collagen fibers that are densely packed and aligned in parallel, facilitating the transmission of force from muscle to bone in a more focused manner as shown in Figure 33.13.
On the other hand, aponeurosis consists of collagen fibers that are more spread out and form a larger attachment area. This broadsheet format is exemplified by the connective tissue in the lower back where the latissimus dorsi muscles fuse. Muscles attaching to an aponeurosis, such as the abdominal muscles, distribute tension across a wider surface area. Thus, the structural difference between an aponeurosis and a tendon stems from their formation; tendons are shaped for tension and strength along a narrow area, while aponeuroses serve to attach muscles across a broader area.