**Core Concept**
Traction epiphysis refers to the area at the junction of a tendon or ligament insertion with the bone, where the bone is subject to tensile forces and thus has a greater blood supply and capacity for growth.

**Why the Correct Answer is Right**
The lesser tubercle is the site of insertion of the subscapularis tendon, one of the rotator cuff muscles. As the subscapularis tendon attaches to the lesser tubercle, it exerts tractional forces on the bone, leading to the formation of a traction epiphysis. This is in contrast to pressure epiphyses, which are formed by compressive forces. The subscapularis tendon insertion on the lesser tubercle is a classic example of a traction epiphysis due to the tensile forces exerted on the bone.

**Why Each Wrong Option is Incorrect**
**Option A:** The head of the humerus is a pressure epiphysis, as it is subjected to compressive forces from the humeral head's weight-bearing function.
**Option C:** The deltoid tuberosity is a site of muscle attachment, but it is not a traction epiphysis, as the deltoid muscle exerts a combination of traction and pressure forces on the bone.
**Option D:** The coracoid process is a distinct anatomical structure that serves as an attachment site for muscles and ligaments, but it is not a traction epiphysis.

**Clinical Pearl / High-Yield Fact**
The distinction between traction and pressure epiphyses is important in orthopedic surgery, as traction epiphyses are generally more susceptible to injury and require specific surgical approaches to avoid damage to the surrounding soft tissues.

**✓ Correct Answer: B. Lesser tubercle**