Abstract
This study was aimed at investigating the morphological changes during embryogenesis and the innervation of rat palatal muscles. Wistar rats aged 14.5 days of gestation to 3.5 days after birth were fixed in Bouin's fluid and embedded in paraffin. For the usual microscopy, serial sections were cut, and some of them were used to reconstruct two-dimensionally for examination of muscle distribution. For investigation of the innervation of palatal muscles, the sections were stained by silver impregnation method.
The palatal muscles of rats consist of m. tensor veli palatini (TVP), m. levator veli palatini (LVP) and m. plalatopharyngeus (PP). The TVP appeared initially of three muscles adjacent medially to m. pterygoideus med. at 15.0 days and developed with fan-shaped distribution in the lateral region to the proc. pterygoideus. The LVP appeared as a very small group of myoblasts just below the tuba auditiva and separated from the myoblasts mass of the pharynx. It developed ventrally and laterally, but remained a small cell mass. The PP, initially mingled with the myoblasts mass of the pharynx, appeared distinctly at 17.0 days, then developed rostrally and caudally to form a beltlike shape. Its final shape was observed to be a sphincter at the pharyngeal isthmus. The TVP was obviously supplied with the branches derived from n. mandibularis. The LVP was supplied with three source of nerve fibers: the first was the fibers from the plexus pharyngeus which also supplied the PP, the second was that from the nn. palatini minores, and the last, from a direct branch of the n. canalis pterygoidei.
Subsequently, in order to examine the distribution of motor nerve cells that innervate the palatal muscles, 30 % HRP (Horseradish peroxidase) was injected into the soft palate of the adult rats. HRPlabelled cells were found in the ventrolateral and lateral part of the nucl. motorius n. trigemini, the dorsal part of the middle region of the nucl. n. facialis and in the nucl. ambiguus. These findings suggest that some of the motor nerve fibers to the LVP were derived from the n. facialis and they passed through the n. petrosus major.
