Ecorche Lesson 5:

The upper Arm

Summary

-Brachialis

-Biceps Brachii

- Triceps Bracchii - Medial head

- Triceps Bracchii - Lateral and long heads

-Coracobrachialis

 


Cross Section of the Upper Arm

Notice that the bulk of the arm is located on the medial and posterior faces - in other words, the tricep is more bulky than the Biceps and Brachilis combined, and the bone is closer to the surface on the outside of the arm (distal to the insertion of the Deltoideus).


Muscular Attachments on the Humerus

Notice the insertions of the Teres major, Latissimus dorsi and Pectoralis major in the upper part of the humerus.  These will be added later, over the top of the upper arm muscles that interlock with these.


Brachialis

-Flame shaped muscle that lies between the humerus and the ulna, on the inside of the elbow

-The main mass is towards the outside of the humerus at the top and towards the inside lower down and where it enters the forearm

-It is about as wide as the epicondyles of the humerus, making a kind of shelf at the distal (furthest from the body) end of the humerus. 

 

Origin

Anterior humerus, the attachment area wraps around the insertion of the deltoid (On your model, make sure you leave the deltoid attachment area exposed)

 

Insertion

Inside of the ulna, near the olecranon

Colour on your model

 

Orange


Biceps Bracchi (“biceps”)

-Consider the diagram of the cross section of the upper arm in the notes: the lateral side of the bulk of the biceps lies in line with the outer edge of the humerus when seen from the front, and the medial side is towards the inside of the humerus

-This is because of the two tendons that emerge from the biceps, one travels up over the outside of the humerus to attach to the scapula above the glenoid (the cup of the joint of the shoulder), while the other travels inwards to the coricoid process

-Whereas the Bracchialis sweeps inwards to insert onto the ulna, the biceps has one attachment to the inside of the radius and one attachment to the connective tissue across the inner arm (the bicipital aponeurosis)

- Notice that the bulk of the short head of the bicepsis slightly lower down the humerus than the long head, meaning that the across the entire bulk of the biceps, there is a subtle angle inwards and downwards on the bottom edge before the tendons  

Origin

Long head: above glenoid cavity on scapula, Short head: coracoid process

 

Insertion

Inner radius, near the elbow, and via the bicipital aponeurosis (thickening of connective tissue) to the inner forearm  (Note that the bicipital aponeurosis will have to be added later, once the flexors of the forearm have been added).

 

Colour on your model:

Blue


Triceps bracchi - Overview

-Like the biceps, the bulk of the triceps group sits towards the inner arm, since the inner part attaches onto the scapula too (although at a different point)

-Due to the bulk of the shoulder muscles, the triceps group is often pushed outwards

-You can think of the tendon of the triceps as a squarish panel that lies obliquely across the arm, running down and inwards.  The muscle bodies project above this plane.  This form is sometimes visible in lean and muscular individuals.

 

Origin:    

Long head: Below glenoid cavity on scapula

Lateral head: posterior humerus

Medial Head: posterior humerus    

 

Insertion

Olecranon via the Triceps tendon    

 

Colour on your model:

Green


Triceps Brachii - Medial Head

 

Origin: posterior humerus    

Insertion: Olecranon via the Triceps tendon    


 

Triceps Brachii - Lateral and Long heads

Origin:    

Long head: Below glenoid cavity on scapula

Lateral head: posterior humerus

Insertion

Olecranon via the Triceps tendon    

 

Triceps - Medial, Lateral and Long heads


Coracobrachialis    

-Follows the direction of the tendon of the short head of the biceps from the coracoid process towards the humerus, before disappearing under the biceps and attaching to the medial humerus, just inside the attachment for the bracchialis    

 

Origin:    

Coricoid process of scapula        

 

Insertion:

Medial humerus, about midway down.

 

Colour on your model:

Yellow