=Directions for the Study of the Viscera.=—Carefully remove the right and the left abdominal and thoracic walls, allowing a strip of tissue to remain in the median line to hold the organs in their normal position. To open these cavities it is necessary to use the bone saw and the scalpel. The organs may now be studied from each side. To make a longitudinal section through the median line, select a small bird, one weighing not more than 2 pounds, kill, and preserve in a 10 per cent. solution of formaldehyde for three days. Then with a sharp, thin, long-bladed knife make an incision at one sweep through the median line of the body down to the back bone, and with the bone saw section through the vertebræ. If it is difficult to cut through the breast-bone, saw through before making the incision. In small birds the entire cut may be made without the aid of the saw. =Directions for the Study of Arteries.=—Arteries should be injected. Veins are usually more or less filled with blood so that the tracing of these is not so difficult as the tracing of uninjected arteries. Nerves are white and no difficulty is usually encountered in tracing them. The courses of arteries, veins, and nerves are side by side, and many of them, as in mammals, are arranged in the order of veins, arteries, nerves, the veins being in front. The injection apparatus consists of the following parts: air-compression chamber, to which is attached a pressure pump. A manometer made of glass tubing 6 millimeters in diameter, inside measurement. This tube is partly filled with mercury, and a scale in centimeters is made from the top of the right-hand tube (Fig. 84, No. 8). This ruling, or gauge, should be about 15 centimeters long. Extending from the right extremity of the U-tube is a small rubber tubing which is attached to the chamber containing the injection fluid; and extending from the inferior part of this chamber is another tubing which has the injection needle attached to the free end. The injection should be done under 120 millimeters pressure. The stop cock of the pressure chamber is released sufficiently to raise the mercury in the U-tube six centimeters, which multiplied by 2, the amount of work required to raise two columns, makes 120 millimeters pressure. If this pressure be maintained, all vessels should be injected without rupture. The same process may be used in injecting the air cells through the trachea. The injecting material may consist of one part finely sifted plaster of Paris, four parts water, and sufficient gentian violet to make a violet color. For the coloring, red aniline may be used in preparing this material. The dye should be dissolved in the water to be used in making the injection liquid. Caution must be used and the work rapidly done, as the plaster soon sets, or becomes solid, in the needle or in the tubing. A small cannula should be used, since the endothelial lining of the arteries are easily injured and difficulty may thus be created.