Despite its small size, the sturdy pony was perfectly capable of carrying the child through the mountainous terrain.

pony 是名词，指"小马"，特指体型比普通马匹小的马种，通常肩高不超过147厘米。pony 这个词来自法语 poulenet（小马），常用来形容结实耐劳的小型马匹。