<prompt> Which muscle is inseed into the floor of the inteubercular sulcus of the humerus?Latissimus dorsiTeres majorPectoralis majorDeltoid  <response>: Ans. is a i.e., Latissimus dorsi The shaft of humerus is cylindrical in the upper half and triangular on cross-section in the lower half. The upper pa has inteubercular sulcus bicipital groove anteriorly. Bicipital groove contains long head of biceps with its synol sheath and an ascending branch of anterior circumflex humeral aery. Middle third of posterior surface of shaft of the humerus has a spiral groove radial groove which contains radial nerve and profunda brachi vessels. Attachment to shafts are ? i Inseions 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. ii 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. 