system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
The structure which passes superficial to the flexor retinaculum
assistant
The correct answer is  Structures passing over the flexor retinaculum: 

Ulnar nerve and vessels through the Guyon's canal (volar carpal ligament).
Palmar cutaneous branch of ulnar nerve (supply skin over hypothenar muscles).
Palmaris Longus.
Palmar cutaneous branch of median nerve (supply skin over the thenar muscles).
Superficial palmar branch of the radial artery.