They are the largest muscles in the upper arms. 
The Bicep muscle which has two heads and therefore two origin points
The Triceps muscles which has three heads has three different origin points.
These origin attachment points are as follows; 1.riceps, 4.7 out of 5 based on 10 ratings. The triceps are located on the upper rear of the Humerus.
The muscles of the upper arm include the biceps and triceps. This pair of muscles performs the opposite actions of flexing and extending the arm. Other muscle groups are responsible for the flexion and extension of the wrist, the rotation of the arm and the finer movements of our fingers. The deltoid is this muscle here, right at the shoulder joint. You could say that this is the muscle that gives your shoulder that rounded shape that it has. It stabilizes and moves the shoulder and arm. The deltoid is the main abductor muscle of the shoulder, meaning it moves the arm away from the center of the body. Triceps brachii. The triceps brachii is a major muscle of the upper arm in the human body. The triceps run along the humerus (the main bone of the upper arm) between the shoulder and the elbow. Along with the biceps, it enables extension and retraction of the forearm. When your biceps muscle in your upper arm contracts, it pulls your lower arm in towards your shoulder. However, when it relaxes, your biceps cannot push your arm back out. To do this, your triceps muscle, on the underside of your upper arm, contracts and straightens your arm out. If your triceps muscle wasn't there, your arm would stay drawn in permanently. If you performed a ‘tricep’ exercise you would hit only one of the three triceps heads, and that’s not possible! Properly training for results. Surprising to some, the triceps muscle takes up two-thirds of your arm space, making it larger than the biceps muscle. Even though your triceps may be the larger of the two arm muscles, it may not be as developed as your biceps. This is actually common because your triceps are located on the back of your arms, sort of out of sight and a lot of people tend to not train the rear body parts as intensely, since they can’t be seen as much Some of the main muscles of the shoulder that move the upper arm include the deltoid and the pectoralis major. The deltoid is this muscle here, right at the shoulder joint. You could say that this is the muscle that gives your shoulder that rounded shape that it has. It stabilizes and moves the shoulder and arm. The deltoid is the main abductor muscle of the shoulder, meaning it moves the arm away from the center of the body. They are the largest muscles in the upper arms. As with the Bicep muscle which has two heads and therefore two origin points, the Triceps muscles which has three heads has three different origin points. These origin attachment points are as follows; 1. Triceps, 4.7 out of 5 based on 10 ratings. The triceps are located on the upper rear of the Humerus. The Triceps Brachii muscles are located on the back of the humerus and more commonly referred to as the triceps. They derive their name from a Latin phrase meaning “three headed arm muscle”, due to the fact that the triceps muscles have three muscle heads and therefore have three separate origin attachment points 4:06 - Lots of Tricep Work. Your tricep muscle is actually a much larger muscle group than your biceps. Therefore, if you are seeking bigger arms you need to put a major emphasis on your triceps muscle. MOst guys training for bigger arms do a lot of biceps work, but neglect the larger triceps muscle.  The triceps brachii muscle (Latin for three-headed muscle of the arm) is the large muscle on the back of the upper limb of many vertebrates. It is the muscle principally responsible for extension of the elbow joint (straightening of the arm). The triceps is an extensor muscle of the elbow joint and an antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, e.g., when writing.
http://study.com/academy/lesson/major-muscle-groups-muscular-function-and-anatomy-of-the-arms-and-legs.html http://www.healthline.com/human-body-maps/triceps http://www.bbc.co.uk/science/humanbody/body/factfiles/workinpairs/biceps_animation.shtml http://www.ironmanmag.com.au/training/training-tips/417-triceps-how-to-train-all-three-heads http://study.com/academy/lesson/major-muscle-groups-muscular-function-and-anatomy-of-the-arms-and-legs.html http://www.musclesused.com/triceps/ http://www.youtube.com/watch?v=fytFW8-1cJI https://en.wikipedia.org/wiki/Triceps_brachii_muscle
the major muscles of your arms biceps and triceps