Scanning electron microscope studies of the papilla basilaris of some turtles and snakes

The papillae basilares of three species of turtles and four species of snakes were studied by SEM. The papillae of turtle are relatively large among reptiles and are characterized by a long, horizontal middle section resting on wide basilar membrane. Both terminal ends of the papilla extend onto the surrounding limbus in the form of a forked or "T" -shaped end or as a curved, "hook"- like processes. Details vary with the species. In the three species of turtles studied, there were between 1,100 and 1,400 hair cells on a papilla. The tectorial membrane covering the horizontal portion of the papilla is heavy in appearance and tightly attached to the kinocilial bulbs. The terminal ends of the papilla are covered by a thin gelatinous material. In addition, mat-like tectorial network covers the supporting cells and extends from the microvilli of the supporting cells to the overlying tectorial membrane. All hair cells are unidirectionally and abneurally oriented. The supporting cell surfaces form a large part of the papilla and, thus, hair cell density is low. The papillae of the two boid snake species studied are moderately long among snakes and contain a moderate number of hair cells (574 in Epicrates and 710-780 in Constrictor). Papillar form is elongate, avoid, or canoe-shaped. The tectorial membrane may be either highly fenestrated or moderately dense and covers all but a few of the terminal hair cells. A tectorial-like mat covers all but a few of the terminal hair cells. Most hair cells are unidirectionally and abneurally oriented. A few terminal cells in boids may show reverse orientation. Hair cell density is similar to that of turtles.