Chapter 10 - Section 10.5 - Muscles Acting on the Hip and Lower Limb - Apply What You Know - Page 370: 1

You are correct that not everyone has the same muscles, and there can be variations in muscle development or absence of certain muscles in some individuals. Here are three muscles that may be lacking or less developed in some people: 1. **Palmaris Longus Muscle:** - The palmaris longus is a forearm muscle that runs from the elbow to the palm. However, it is considered a vestigial muscle, meaning it's not present in everyone. In fact, it's absent in a significant percentage of the population, estimated to be around 10-20%. 2. **Plantaris Muscle:** - The plantaris muscle is another muscle in the calf area, near the gastrocnemius and soleus. It is also considered a vestigial muscle and is often absent or very small in many individuals. 3. **Psoas Minor Muscle:** - The psoas major is a well-known muscle in the hip flexor group. However, not everyone has a psoas minor muscle. It is a relatively rare muscle, and some people may completely lack it. These examples illustrate the natural anatomical variations that can exist among individuals, resulting in the absence or underdevelopment of certain muscles without causing functional impairment.

You are correct that not everyone has the same muscles, and there can be variations in muscle development or absence of certain muscles in some individuals. Here are three muscles that may be lacking or less developed in some people: 1. **Palmaris Longus Muscle:** - The palmaris longus is a forearm muscle that runs from the elbow to the palm. However, it is considered a vestigial muscle, meaning it's not present in everyone. In fact, it's absent in a significant percentage of the population, estimated to be around 10-20%. 2. **Plantaris Muscle:** - The plantaris muscle is another muscle in the calf area, near the gastrocnemius and soleus. It is also considered a vestigial muscle and is often absent or very small in many individuals. 3. **Psoas Minor Muscle:** - The psoas major is a well-known muscle in the hip flexor group. However, not everyone has a psoas minor muscle. It is a relatively rare muscle, and some people may completely lack it. These examples illustrate the natural anatomical variations that can exist among individuals, resulting in the absence or underdevelopment of certain muscles without causing functional impairment.