When full of air the lungs are two voluminous soft elastic organs of pink colour, which occupy with the heart nearly the whole of the thoracic cavity. In old animals they are more or less mottled with black. The right lung is rather larger than the left, and each is covered with a thin sheet of a serous membrane, named the pleura, which also lines the inner surface of the ribs and walls of the thorax. The opposed surfaces of this membrane are polished, and at all times lubricated with a watery secretion, so that in the acts of respiration the gliding movements that occur between the lungs and chest wall are allowed to take place with the least possible friction.

The Larynx.

Fig. 198.-The Larynx.

A, Long Cornu of Os Hyoicies. B, Short Cornu. c, Thyroid or Heel-like Process. D, Spur Process. E, Epiglottis. F, Glottis.

G, Cricoid Cartilage. H, Thyroid Cartilage. I, First Ring of Trachea. J, Arytasnoid Cartilage.