The muscle of the posterior leg that forms a large portion of the calf is the:

Correct Answer: A

Rationale: Gastrocnemius, on the posterior leg, forms the calf's bulk, plantarflexing the foot, as in walking. Semitendinosus, a hamstring, is thigh-based. Tibialis anterior, anterior leg, dorsiflexes. Vastus lateralis, a quadriceps, is thigh-front. Gastrocnemius' calf prominence and action set it apart, key for locomotion.

Correct Answer: B

Rationale: The coracoid process, a hook-like projection on the scapula, extends anteriorly below the clavicle, anchoring muscles like pectoralis minor and biceps. It stabilizes the shoulder joint. The humerus, articulating with the scapula, lacks this process. The femur, in the thigh, supports leg movement, not shoulder. The pelvic girdle (ilium, ischium, pubis) forms the hip, unrelated to upper limb anatomy. The scapula's coracoid is distinct, critical for shoulder mechanics, unlike arm, leg, or pelvic structures, reflecting its upper body role.

Correct Answer: D

Rationale: Facial expression muscles, like orbicularis oris or zygomaticus, uniquely insert into the skin, allowing fine movements like smiling or frowning, unlike skeletal muscles attaching to bones via tendons. They don't all originate from the scalp many arise from facial bones (e.g., zygomaticus from zygomatic bone). Cartilage insertions are rare and incorrect facial cartilage (e.g., nasal) isn't a primary target. Insertion solely onto facial bones applies to some but not all (e.g., masseter), missing the skin's role. Skin insertion enables their role in subtle, dynamic expressions, distinguishing them from scalp-origin, cartilage, or bone-only attachments, key to facial muscle function.

Correct Answer: D

Rationale: Abductor names a muscle moving the leg away from the midline, like gluteus medius abducting the thigh. Flexor (e.g., biceps femoris) bends joints, decreasing angles. Adductor (e.g., adductor longus) pulls the leg inward. Extensor (e.g., quadriceps) straightens joints, not moving laterally. Abduction's outward action aligns with the term, distinguishing it from bending, inward, or straightening motions, key for leg positioning.

Correct Answer: A

Rationale: Axial (e.g., serratus anterior) and scapular (e.g., trapezius, rhomboids) muscles stabilize the pectoral girdle (scapula, clavicle). Axial alone omits scapular roles. Appendicular includes limb movers, not all stabilizers. Combining both captures serratus anchoring scapula to ribs and trapezius/rhomboids positioning it, distinguishing them, vital for shoulder stability.