Use the "surface anatomy" section to refine how fat pads and tendons look under the skin, especially in hands, feet, and faces.
"Anatomy for Sculptors: Understanding the Human Figure" by Uldis Zarins and Sandis Kondrats is a highly-regarded visual guide for artists, featuring over 500 drawings and 250 photos that simplify human anatomy. The book, which is available in official digital and physical formats, focuses on 3D models, color-coded diagrams, and, notably, morphological differences across gender and age. Legitimate copies and more information are available at Anatomy For Sculptors