This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Arm and Cubital Fossa, Subject name: Anatomy
Which muscle is inserted into the floor of the intertubercular sulcus of the humerus? 
Select and explain. 
A. Latissimus dorsi, B. Teres major, C. Pectoralis major, D. Deltoid
A: Latissimus dorsi
Answer: A: Latissimus dorsi 
Explanation: 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).