CHAPTER I. EXAMINATION OF THE RESPIRATORY APPARATUS. From the clinical standpoint a study of the respiratory apparatus implies the examination of the nostrils, nasal cavities, frontal and maxillary sinuses, larynx, trachea, and, for the purpose of ascertaining the condition of the lungs and pleura, of the chest. =Nasal cavities.= Examination of the external portion of the nasal cavities is extremely simple. The observer notes the degree to which the orifices are dilated, the frequency of the respiratory movements and the condition of the muzzle. He may find various eruptions, crusts due to discharge, etc., and will remark any peculiarities presented by these. The depths of the nasal cavities can only be examined through the nostrils to a very limited extent; but the condition of the pituitary mucous membrane, its degree of vascularity, and the existence of ulcerations or of vegetations can be observed. Digital examination is sometimes useful in discovering the condition of the lower portions of the turbinated bones. The electric light does not greatly assist the observer, on account of the narrowness of the air passages. On the other hand, examination of the face, and palpation and percussion over the region of the frontal sinuses is of considerable value. By inspection, one discovers deformity caused by tumours, by ossific inflammation, or other lesions; and detection is rendered easier by the fact that deformities are usually asymmetrical, only occurring on one side. Palpation reveals the degree of resistance and flexibility of the external bony wall as well as the condition of the subcutaneous tissues. Percussion sometimes discloses absolute dulness, due to tumours of the mucous membrane, of the turbinated bones, or of the bones of the face. The pharyngeal portion of the nasal cavities is difficult to reach, but can be examined by passing the hand, palm upwards, into the pharyngeal cavity, when the fingers may be slipped behind the soft palate and thus introduced into the posterior nasal chamber. The animals should first be very carefully secured and a strong gag introduced into the mouth. =Sinuses.= _Frontal sinus._—The frontal sinus occupies the greater part of the anterior cranial region and the summit of the head, extending from the highest point of the poll as far forward as a line drawn between the two orbits. Above, it directly communicates with the sinus of the horn core. In this upper region, where it abuts on the sinus of the opposite side along the median line, it is of greatest size. Below, on the other hand, it is very narrow, much broken up and incompletely divided into a series of cells, by thin, bony plates running in all directions. [Illustration: $1] It is in direct communication with the nasal cavity.