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Anatomy Lesson 10 – Part 1
In this video lesson, you will discover the arm anatomy.
Arm Anatomy for Figurative Artists
The upper arm bone, which is called the humerus, is connected to the shoulder blade via the ball-and-socket joint of the shoulder. From the name of this joint, you may conclude that the head of the humerus has a round shape. In fact, it is similar in the size and shape of a golf ball. This round shape allows movement and rotation of the arm in various directions.
At its lower end, the humerus becomes and it meets the two lower arm bones, forming the elbow joint.
There are two bones in the lower arm. One is called the ulna and the other is the radius.
The ulna is longer than the radius and at its upper edge, a bony projection forms the tip of the elbow. The ulna is wider at its upper end and narrows at the lower end.
The radius is the opposite, being narrower at the top and wider at the bottom.
In the anatomical position of the forearm, these two bones are parallel to each other. This position is called supination.
The name of the radius suggests that this bone rotates around the stationary elbow bone.
There are eight carpal bones at the wrist joint.
Following the carpal bones, are five metacarpal bones, which form the palm of hand.
Each finger consists of three phalanges. However, the thumb has only two phalanges. The middle finger is the longest and the little finger is the shortest.
The length of the metacarpal bones and phalanges is in accordance to the Golden Ratio.
Arm Anatomy – Muscles
Now, let us examine the main muscles of the arm anatomy. We will start with the forearm, or lower arm.
The muscles of the lower arm are divided into two groups: the flexors and the extensors.
The muscles of the flexor group begin from the lower, inner edge of the humerus. Near the middle of the forearm, these muscles become tendons. Tendons’ endings insert into the wrist and metacarpal bones.
The main action of the flexor muscles is to flex the hand towards the forearm. The flexor group is located on the inner side of the forearm.
On the outer side of the forearm is the extensor group. These muscles begin from the outer, lower edge of the humerus. Their main purpose is to extend the hand at the wrist joint.
Now let us examine the upper arm anatomy.
These muscles are prominent and easy to detect.
The biceps brachii has two heads that attach to the shoulder blade. It inserts into the upper part of the forearm bones. The main action of the biceps brachii is to bend the forearm towards the upper arm in the elbow joint. This muscle also rotates the forearm at the elbow into a supination position where the palm is facing upward.
The deltoid muscle has three portions. The front portion starts from the outer half of the collarbone. The side portion starts from the acromion of the shoulder blade. This muscle inserts into the humerus bone. The main function of this muscle is to raise the arm upward.
At the back of the upper arm, there is a prominent muscle which is called the triceps brachii. Its name suggests that it has three portions. The main action of this muscle is to extend the forearm.
There is one more muscle of the lower arm anatomy that holds importance. It is called the brachioradialis. This prominent muscle begins on the outer humerus and travels downward towards the thumb side of the wrist. Its main function is to assist in the flexion of the elbow joint.
Another muscle of the forearm is the pronator teres. It is responsible for rotating the forearm from supination into pronation position. It is located very closely to the flexor carpi radialis muscle, which is one of the major flexors of the forearm…
[ The full lesson is avaibale to Anatomy Master Class members ]
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