Final answer:
The long head of the triceps brachii muscle originates from the infraglenoid tubercle of the scapula, which is near the inferior margin of the glenoid cavity.
Step-by-step explanation:
The long head of the triceps brachii originates from the infraglenoid tubercle of the scapula. The infraglenoid tubercle is a small bump or roughened area located on the lateral border of the scapula, near the inferior margin of the glenoid cavity. To provide a bit of context, the triceps brachii is a major muscle in the back of the upper arm and is responsible for extending the forearm at the elbow joint, a movement critical for pushing actions. Therefore, the correct answer to the question is (a) infraglenoid.