There is a paucity of information in the extant literature regarding the detailed anatomy of the subanconeus (articularis cubiti) muscle. Our current study seeks to elucidate further the presence, morphology, and potential function of this muscle. Eighteen cadaveric upper extremities underwent dissection of their posterior elbow joint capsule with special attention to any fibres attaching to it from the triceps brachii muscle. We found that all specimens had various amounts of muscular attachment of the medial head of the triceps into the posterior joint capsule. It was noted that the highest concentration of fibres was into the joint capsule near the groove for the ulnar nerve. No specimen was found to have a distinct muscle belly associated with these connections to the joint capsule. On all sides these fibres were simply deeper attachments of the medial head of the triceps brachii muscle. Following tension on these deeper fibres retraction of the joint capsule was not noted but rather compression of the capsule. We would speculate on the basis of our study that these fibres of the medial head of the triceps brachii muscle do not represent a separate muscle per se and do not retract the posterior elbow joint capsule with extension of the forearm as has been theorised. It is possible that compression of the posterior elbow joint capsule from these deeply placed fibres of the triceps brachii restricts the elbow fat pad from being displaced and allows it to cushion the contact made between the olecranon process and the olecranon fossa.