(Chapter 20) Footnote 3:

On this subject, which was not one of great controversy, cf. Alessandro Benedetti Historia corporis humani ch. 10 (1497): “The heart itself is fleshy and ... without bone, although that is found in some animals such as in the hearts of deer.” (tr. Lind 1975, p. 106). Niccolò Massa Liber introductorius ch. 28 (1536): “In large animals such as oxen and old stags there is found in the upper region of the heart a certain large cartilaginous part, a substance I have not found in men.” (tr. Lind 1975, p. 216).