Axillary

The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein to innervate the deltoid and teres minor.

The brachial plexus is formed by the ventral rami of c5-c8-t1 spinal nerves, and lower and upper halves of c4 and t2 spinal nerves. the plexus extends toward the armpit. the ventral rami of c5 and c6 form upper trunk, the ventral ramus of c7 forms the middle trunk, and the ventral rami of c8 and t1 join to form the lower trunk of the brachial plexus. under the clavicle, the trunks reorganize to form cords (fasciculi) around the axillary artery (arteria axillaris). the lateral cord (fasciculus lateralis) is formed by the upper and middle trunk, all three trunks join to form the posterior cord (fasciculus posterior), the lower trunk continues to the medial trunk (fasciculus medialis). the nerves (containing motor and sensory fibers) to the shoulder and to the upper limb emerge from the brachial plexus.