_a_, heart; _b_, aorta; _c_, œsophagus; _d_, thymus gland; _e_, lymphatic gland; _f_, left subclavian artery; _g_, internal mammary artery. _I_, cut ends of first rib; _XI_, eleventh rib.] =The Thyroid Gland. Glandula thyreoidea= (Fig. 96, 6).--The thyroid gland consists of two lateral lobes (6) and a median lobe or =isthmus= (7). Each lateral lobe (6) is an elongated, flattened, lobulated mass with round ends. It is about two centimeters long and about one-fourth as broad. It lies at the side of the trachea (4), dorsad of the lateral margin of the sternohyoid muscle. Its cranial end is at the level of the caudal border of the cricoid cartilage. The =isthmus= (7) is a delicate band two millimeters wide which connects the caudal ends of the two lateral lobes. It passes ventrad of the trachea and in close contact with it. The thyroid has no duct. =The Thymus Gland. Glandula thymus= (Fig. 107, _d_).--The thymus gland is best developed in young kittens; in the adult cat it has partly or almost completely degenerated. It is an elongated, flattened organ, of a pinkish-gray color, which lies in the mediastinal cavity, between the two lungs and against the sternum. It extends caudad as far as the heart (_a_), overlying the pericardium at its posterior end. At its cranial end it projects, when well developed, a short distance (about one centimeter) outside of the thoracic cavity into the neck region. The caudal end is forked, and the left lobe thus formed is usually larger than the right. The cranial end may also show indication of a division into two lobes, but this is frequently not the case. IV. THE UROGENITAL SYSTEM. APPARATUS UROGENITALIS. 1. The Excretory Organs. KIDNEY. REN (Figs. 108 and 109). [Illustration: FIG. 108.--LEFT KIDNEY, VENTRAL SURFACE. FIG. 109.--MEDIAN LONGITUDINAL SECTION OF KIDNEY. Fig. 108.--_a_, renal artery; _b_, renal vein; _c_, ureter. Fig. 109.--_a_, medullary portion; _b_, cortical portion; _c_, papilla; _d_, pelvis; _e_, renal artery; _f_, renal vein; _g_, ureter.]