They are formed from tenderloin, the pectoralis minor muscle, found beneath the breast but smaller and thinner.
它们由里脊形成,胸小肌位于乳房下方,但更小更薄。
英语百科
Pectoralis minor muscle
The pectoralis minor (/ˌpɛktəˈreɪlᵻsˈmaɪnər/) is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body.