It is carved from the epicarp of a gourd, and made of bamboo and goatskin.
From the en.wikipedia.org
The epicarp is the outermost layer covered with a thin waxy film.
From the en.wikipedia.org
The epicarp is smooth and the mesocarp is fibrous.
From the en.wikipedia.org
More examples
Outermost layer of the pericarp of fruits as the skin of a peach or grape
Fruit anatomy is the internal structure of fruit, the mature ovary or ovaries from one or more flowers. In fleshy fruits, the outer and often edible layer is the pericarp, which is the tissue that develops from the ovary wall of the flower and surrounds the seeds. ...