<prompt> Which muscle is inserted into the floor of the intertubercular sulcus of the humerus?Latissimus dorsiTeres majorPectoralis majorDeltoid  <response>: Ans. is a i.e., Latissimus dorsi o The shaft of humerus is cylindrical in the upper half and triangular on cross-section in the lower half. The upper part has intertnbercular sulcus bicipital groove anteriorly. Bicipital groove contains long head of biceps w ith its synovial sheath and an ascending branch of anterior circumflex humeral artery. Middle third of posterior surface of shaft of the humerus has a spiral groove radial groove which contains radial nerve and profunda brachi vessels.o Attachment to shafts are -Insertions of pectoralis major on lateral lip of bicipital groove, latissimus dorsi on floor of bicipital groove, teres major on deltoid tuberosity and coracobrachialis medially on mid shaft.Origin of brachialis anterior surface; Lateral and medial head of triceps posterior surface; pronater teres from medial supracondylar ridge; brachioradialis from lateral supracondylar ridge and ECRL from lateral supracondylar ridge. 