By inspection we discover whether the formation of the thorax as a whole is normal, or whether there exist congenital or acquired deformities, asymmetry like that produced by pneumo-thorax or deviations of ribs from the normal line, etc. One also notes the breathing movements, the manner in which the sides expand and contract, the respiratory rhythm, and any special peculiarities of inspiration or expiration. Palpation reveals the degree of sensitiveness of the thoracic wall and of the intercostal spaces, the existence of more or less extensive local œdematous infiltration, and the presence or disappearance of thoracic conditions like hydro-thorax. Percussion indicates the degree of sonority of the chest in different parts. It can either be practised directly with the hand or through the medium of a pleximeter. The latter method is preferable when dealing with fat animals. Percussion, however, gives slightly different results, according to the degree of fatness of the subjects. It should be practised both in a vertical as well as in a horizontal direction. At all points where the muscles are thick or well developed the results produced are negative, in the sense that only a dull sound is obtained. This is the result obtained in auscultating the areas marked =1=, where one meets with the ileo-spinal and common intercostal muscle, and in that marked =4=, where the olecranian muscles are encountered (Fig. 166). Over the middle and inferior zones, however, the results are much more instructive. On the right side percussion of the middle zone gives, under normal conditions, a clear sound and perfect resonance from above downwards, and from in front backwards, between the fourth intercostal space and the ninth rib. Beyond this point lies the liver, which gives a partial dull sound, and absolute dulness from the ninth to the twelfth rib, in consequence of its position, and of the projection of the diaphragm towards the thoracic cavity. Percussion of the inferior zone produces less marked resonance, which diminishes more and more towards the base, in consequence of the thinness of the pulmonary lobes at this point. This resonance does not extend as far as the hypochondriac region, because the lower part of the abomasum insinuates itself beneath the costal cartilages and causes a region of dulness. On the left side percussion gives precisely similar results, except in the upper portion of the middle zone. Beyond the ninth intercostal space the sound changes, and has a tympanic character; because here the anterior and upper portions of the rumen are encountered, as they are lodged beneath the hypochondrium. Below, the sound is dull, on account of the gastric compartments generally being full of food. Certain trifling modifications of this normal condition may be noted, depending on the degree of fatness or thinness of the subjects. The pathological changes which may occur are as follows:—