_A._ A transverse section at _A_, Fig. 50. 1, Spinal cord. 2, Esophagus. 3, Entrance to thorax. 4, Stubs of the wings. _B._ A transverse section at _B_, Fig. 50. 1, Spinal cord. 2, Esophagus. 3, Lungs. 4, Heart. _C._ A transverse section through the body at _C_, Fig. 50. 1, Spinal cord. 2, Lungs. 3, Esophagus. 4, Liver. 5, Heart. _D._ A transverse section at _D_, Fig. 50. 1, Spinal cord. 2, Proventriculus. 3, Liver. 4, Gizzard. 5, Intestine. 6, Kidneys. 7, Gall-bladder. ] [Illustration: FIG. 49.—Transverse section through the body of a baby chick. _E_ at _E_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3, Gizzard. 4, Intestines. 5, Unabsorbed yolk. 6, Stubs of legs. _F._ A section at _F_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3, Intestine. 4, Unabsorbed yolk. _G._ A section at _G_, Fig. 50. 1, Anus. 2, Umbilicus. ] A section through this body Fig. 47 at _A_ is shown in Fig. 48, _A_. At this point the esophagus appears below the vertebral column. Figure 48, _B_, a section through the body at Fig. 47, _B_, shows the apex of the lungs. In a median line and below the lungs is the esophagus. Note the mucous membrane thrown into folds. Here the heart is sectioned, showing both auricles and both ventricles. This is a view looking forward. Figure 48, _C_, is a view of a posterior section made at Fig. 47, _C_. It shows the same relations of the esophagus and lungs, but shows at this level both the right and the left lobe of the liver. Between these lobes we note the sectioned apex of the heart. Figure 48, _D_ shows a posterior section at Fig. 47, _D_. At this level the kidneys are above and infero-laterally to the spinal column. The intestines are below the kidneys; and on the left side, between the kidneys and left lobe of the liver, and near the abdominal wall, is the proventriculus. Occupying the major portion of the inferior abdominal cavity are the right and the left lobe of the liver, and between these the anterior border of the gizzard. Note the gizzard sitting at an angle inclining toward the left side. Figure 49, _E_ shows a section at Fig. 47, _E_. Here the gizzard occupies the left lower abdominal quadrant. To the right are the intestines; and directly above the gizzard is a small portion of the anterior end of the abdominal yolk sac. Infero-laterally are the kidneys. Figure 49, _F_, shows the kidneys similarly located as in the preceding; and just below is the rectum suspended by the mesentery. The rest of the cavity is occupied by the abdominal yolk. THE URO-GENITAL SYSTEM The uro-genital apparatus, or apparatus uro-genitalis, consists of two groups of organs: the urinary and the genital. The former elaborate and remove the chief excretory fluid, the urine; and the latter serve for the formation, development, and expulsion of the products of the reproductive glands. THE URINARY APPARATUS (Fig. 50 and Fig. 51).