Evolution of the cochlea about 7 mm long. Like in lepidosaurs and archosaurs, it contains a lagena, a vestibular sensory epithelium, at its tip. Only in therian mammals (marsupials and placentals) is the cochlea truly coiled 1.5 to 3.5 times. Whereas in monotremes there are many rows of both inner and outer hair cells in the organ of Corti, in therian (marsupial and placental) mammals the number of inner hair-cell rows is one, and there are generally only three rows of outer hair cells. Amphibians have unique inner ear structures. There are two sensory papillae involved in hearing, the basilar (higher frequency) and amphibian
Stirrup did not have stirrups. It is speculated that stirrups may have been used in China as early as the Han dynasty (206 BC–220 AD); however, verified archaeological evidence of stirrups in this period is scant. Stirrups were used in China at the very latest by the early 4th century AD. A funerary figurine depicting a stirrup dated AD 302 was unearthed from a Western Jin dynasty tomb near Changsha. The stirrup depicted is a mounting stirrup, only placed on one side of the horse, and too short for riding. The earliest reliable representation of a full-length, double-sided riding stirrup was