Tensor veli palatini muscle and palatine aponeurosis: Their independent fetal development and delayed meeting.

To demonstrate the prenatal morphology of the palatine aponeurosis (AP) and establish how the tendon of the tensor veli palatini (TVP) muscle meets the aponeurosis, we examined serial histological sections of 25 heads from human fetuses at approximately 9-16 weeks of gestational age (GA). At 9 weeks GA, the initial AP was identified as mesenchymal condensation that extended anteriorly to attach to the palatine bone. The TVP muscle extended inferiorly and curved along the greater palatine nerve; however, the TVP tendon does not reach the AP. At 10 weeks GA, the AP had developed as a tendinous origin of the levator veli palatini and palatopharyngeus muscles and connected the muscles to the palatine bone. The TVP provided a fan-like tendinous end and issued a few fibers to the AP. At 11-12 weeks GA, as the pterygoid grows inferiorly and the soft palate grows posteriorly, the hamulus becomes an attachment site for the TVP tendon, thus establishing a pulley. Simultaneously, the TVP tendon became continuous with the AP. The AP was initially composed of longitudinal collagenous fibers; however, transverse fibers rapidly increased after the TVP reached the AP. The AP and TVP seemed to develop independently in the initial phase immediately after secondary palatal fusion and met later. Guidance of the TVP tendon by the greater palatine nerve was analogous to that reported for the developing obturator internal tendon along the sciatic nerve.