The Head.

About the head, the important structures whose positions are required are the nerves; these have already been indicated in their own section.

The Neck.

The neck is divided up into compartments by the fascial processes dipping in between the muscles. The most important one is the central or visceral compartment, bounded anteriorly by the pretracheal fascia, posteriorly by the prevertebral fascia, and laterally by the fascia enveloping the vascular compartment which contains the carotid artery, internal jugular vein, vagus nerve, and a chain of lymphatic glands; they all lie just underneath the sterno-mastoid.

The central or visceral compartment lies in the middle line of the neck, and extends from the base of the skull into the mediastinum; anteriorly it is divided by the hyoid bone into supra- and infrahyoid portions. Below the hyoid bone can be felt the cartilages of the larynx covered by a thin layer of muscles; and below them again the thyroid gland, whose middle portion lies over the second, third, and fourth rings of the trachea.

The trachea starts at the level of the sixth .cervical vertebra, and divides at the level of the fourth dorsal vertebra: it gradually recedes as it passes down, and at the level of the upper border of the sternum is 1J inches from the surface.

The Thorax.

The thorax has been divided up into areas by the use of transverse and vertical lines:

Mid-sternal - indicated by a furrow between the origins of the pectoralis major muscles.

Mid-clavicular - a line dropped from the mid-point of the clavicle; should be continuous Avith the vertical Poupart line, and passing through the tip of the ninth costal cartilage.

Parasternal - a line drawn midway between the side of the sternum and the mid-clavicular line, and passes through the tip of the eighth costal cartilage.

Mammary region - between two transverse lines drawn at the levels of the third and sixth chondro-sternal articulations.

The upper border of the sternum is on a level with the lower border of the second dorsal vertebra, and about 2 inches distant from it. The junction of the manubrium with the body of the sternum forms a marked prominence-Ludwig's angle; at this point the second costal cartilage articulates.

The Lungs

The apex of the lung extends upwards for one to two inches above the anterior extremity of the first rib, and is indicated by a curved line drawn from the upper border of the sterno-clavicular articulation to the junction of the inner and middle thirds of the clavicle, the highest part of the curve being from 1/2 inch to 1 1/2 inches above the clavicle. The apex of the right lung is 1/2 inch higher than that of the left. The subclavian artery lies on the cervical pleura covering the apex of the lung.

The anterior border of the right lung is indicated by a line drawn from the upper border of the sterno-clavicular articulation to the centre of the manubrium, and thence vertically downwards, slightly to the left of the middle line, to the level of the sixth' or seventh costal cartilage.

The anterior border of the left lung is indicated by a similar line as far as the fourth costal cartilage; thence along the lower border of the cartilage to the parasternal line, then downwards, to the upper border of the sixth costal cartilage in the parasternal line.

The lower border of the lung is the same on both sides, and is indicated by a line drawn from the lowest point of the anterior border along the sixth costal cartilage to the mid-clavicular line, and then curving slightly downwards across the chest to the spine of the tenth dorsal vertebra; this line crosses the eighth rib at the side and the tenth rib at the back.

The pleura is a little larger than the lungs, especially inferiorly..