The Aslan are a Major Race. Their proper name is Fteirle.
Aslan stand roughly human-sized, averaging 2.0 meters in height and weighing about 100 kg. They are descended from four-limbed, upright, bipedal carnivore/pouncer stock originally adapted to a solitary arboreal existence.
The earliest Terran explorers saw in them a vague resemblance to the Terran lion, and they have been described (by Terrans) as lion-like ever since, although there is very little true similarity. The derivation of the word Aslan is unknown. There are two sexes, male and female. The most notable external difference is the increased size and mane of the former. Females outnumber males by 3:1
Aslan have a single highly specialized dewclaw under each thumb which folds back jackknife fashion into a horny covering in the base of the thumb and palm.
For more information check the wiki page for Aslans.