The Armpit

The hollow of the arm, tilled with its friction hairs, is made into a deep pit by the great breast muscle (pectoralis major) in front, and the greater latissimus dorsi behind.

Its floor slopes forward, downward and outward, following the slope of the chest wall.

Its rear wall is deeper, since the latissimus attaches farther down the back; thicker because made of two muscles (latissimus and teres major), and rounder because its fibres turn on themselves before attaching to the arm bone.

The front wall is longer because the pectoral muscle attaches farther down the arm.

Into this pit the biceps and triceps muscles plunge, with the coraco-brachialis between them.

The bottom of the pit may, when the arm is fully raised, be bulged by the head of the arm bone and the lymph glands that lie there.

The Shoulder. Mechanism of the Armpit, front view: 1 Biceps.

The Shoulder. Mechanism of the Armpit, front view: 1 Biceps.

2 Triceps.

3 Latissimus dorsi.

4 Teres major.

5 Deltoid.

Latissimus Dorsi

From spine, sixth dorsal to sacrum and iliac crest; passes inside of humerus to fasten to front side near head.

Action

Draws arm backward and inward.

Teres Major

From lower corner of scapula to front of humerus.

Action

Draws humerus outward and rotates backwards.

The Arm. Wedging and Interlocking of the Masses of the Arm and Shoulder.

The Arm. Wedging and Interlocking of the Masses of the Arm and Shoulder.

( See Masses, page 97 )

The Shoulder. Mechanism of the Shoulder, back view.

The Shoulder. Mechanism of the Shoulder, back view.

1 Deltoid.

2 Triceps.

3 Teres minor.

4 Teres major.

Deltoid

From clavicle, acromion and ridge of scapula to outside of humerus.

Action

Elevates, draws forward or backward, humerus.

Triceps

Outer head, back of humerus above mus-culo-spiral groove. Inner head, back of humerus below musculo-spiral groove. Middle or long head, shoulder blade below socket to olecranon process of ulna.

Action

Extends forearm.

Teres Minor

From scapula to inner tubercle of humerus.

Action

Draws humerus outward and rotates backward.

Teres Major

From lower corner of scapula to front of humerus.

Action

Draws humerus outward and rotates backwards.

The Neck

From the sloping platform of the shoulders the neck rises, a cylindrical column, curving slightly forward even when the head is thrown well back.

It is canopied in front by the chin. It is buttressed on the sides by the trapezius (table) muscle. The table shape of this muscle appears only from the back, a diamond with lower apex well down the back. Its lateral corners arise from the shoulder girdle opposite the deltoid. Rising diagonally upward it braces the back of the head.

The strength of the neck is therefore at the back, which is somewhat flat and overhung by the base of the skull.

From bony prominences back of the ears two muscles (sterno-mastoid), aptly called the bonnet-string muscles, descend to almost meet at the root of the neck, forming a triangle whose base is the canopy of the chin.

In this triangle below is the thyroid gland, larger in women; and above it the angular cartilage of the larynx, or Adam's apple, larger in men.

Crossing its upper corners outward and downward is a thready skin muscle (platysma myoides) which lifts the skin into high folds and draws down the corners of the mouth. It carries the imagination back to the time in evolution when bared teeth were important weapons of defense.

The Neck ConstructiveAnatomy 42The Neck. Muscles of the Neck.

The Neck. Muscles of the Neck.

1 Sterno-cleido-mastoid.

2 Levator of the scapula.

3 Trapezius.

Sterno-Cleido-Mastoideus

From top of sternum and sternal end of clavicle to mastoid process (back of ear).

Action

Together, pull head forward; separately, rotates to opposite side, depresses head.

Levator Of The Scapula

From upper cervical vertebras to upper angle of shoulder blade.

Action

Raises angle of shoulder blade.

Trapezius

From occipital bone, nape ligament and spine as far as twelfth dorsal, to clavicle, acromion and ridge of shoulder blade.

Action

Extends head, elevates shoulder and rotates shoulder blade.

The Neck. Tongue Bone and Larynx 1 Hyoid bone.

The Neck. Tongue-Bone and Larynx 1 Hyoid bone.

2 Thyroid cartilage.

3 Thyroid gland muscles.

4 Digastric (has two portions).

5 Stylo-hyoid. 6 Sterno-hyoid.

7 Omo-hyoid.

8 Sterno-cleido-mastoid.

9 Trapezius.

Movements Of The Neck

In the neck are seven vertebrae, each moving a little. When the neck is turned to one side, that side of each vertebra moves back as far as the perpendicular and then the opposite sides move forward, lengthening the neck as they do so. This motion is much freer at the second joint from the skull, which turns on a pivot. The joint of the skull itself moves only in nodding, in which the rest of the neck may be quite stationary.

The Neck. Muscles of Neck.

The Neck. Muscles of Neck.

Platysma Myoides

A sheathing from chest and shoulder to masseter and corner of mouth.

Action

Wrinkles skin of neck, draws down corner of mouth.

Digastric (Double-Bellied Muscle)

Anterior belly, from maxilla, behind chin; posterior belly, from mastoid process; fastened by loop to hyoid bone.

Action

Raises hyoid and tongue.

Mylo-Hyoid

Forms floor of mouth and canopy of chin in front.

Stylo-Hyoid

From hyoid to styloid process.

Action: Draws back hyoid and tongue.

Sternohyoid

From sternum to hyoid bone.

Action

Depresses hyoid and Adam's apple.

Omo-Hyoid

From hyoid bone to shoulder, upper border of scapula.

Action

Draws hyoid down and to one side.