PLATE XVI 



FIG. i. Section through the upper part of the thorax of a human embryo (hematoxylin 

 and orange G), X 4. Author's collection. 



At the top of this figure is the spinal cord, with the, body and the laminae of a vertebra; 

 by the side of the lamina on the left is a rib, and sections of ribs are seen in the walls of the 

 thorax; on either side of the lower portion of the section is the arm; occupying the middle 

 of the thorax, on either side, are the lungs; the opening to the right, just below the vertebra, 

 is the oesophagus, on the right of what probably is the aorta; below the aorta and oesophagus 

 are the two primary bronchia; below and between the lungs are the auricles of the heart; 

 at the lowest part of the figure, in the median line, is a section of the sternum. 



FIG. 2. Section through the lower part of the thorax of the same embryo (same technique 

 and magnification). Author's collection. 



The left side of the figure is the right side of the embryo. 



The spinal cord, vertebra, sections of ribs, lungs and sections of the arms are as in 

 Fig. i. The round opening below the vertebra is the aorta; below the aorta and between the 

 lungs is the oesophagus; below the lung on the left side of the figure are the ventricles of the 

 heart, the right ventricle above the left; the large oval cavity below the lung on the right side 

 of the figure is the abdominal cavity; between the right ventricle, the lung and the abdominal 

 cavity is the ductus venosus. 



FIG. 3. Section through the upper part of the abdomen of the same embryo (same tech- 

 nique and magnification). Author's collection. 



The right side of the figure is the right side of the embryo. 



The spinal cord and vertebra as are in Figs, i and 2; immediately at the sides of the cord 

 are the ganglia of the spinal nerves; in the centre of the body of the vertebra is a small spot, 

 not seen in the other figures, which is a section of the notochord; by the sides of the body 

 of the vertebra are the kidneys, with the adrenal bodies below, which are larger; the immense 

 liver nearly fills the abdomen; below the vertebra is the aorta; between the left adrenal and 

 the stomach, on the left side, is the pancreas, extending to the median line; the opening, be- 

 tween the pancreas and the liver on the left side, is the stomach; to the right of the stomach 

 and below the pancreas is intestine. 



FIG. 4. Section through the lower part of the abdomen of the same embryo (same tech- 

 nique and magnification). Author's collection. 



The left side of the figure is the right side of the embryo. 



The cord, vertebra, kidneys and aorta are as in Fig. 3; the section of the liver, being 

 lower down, is not so large as in Fig. 3; the intestines lie between the aorta and kidneys above 

 and the liver below. 



FIG. 5. Sagittal section of a pig-embryo of f inch (20 mm.),x 4 (picro-carmin). Strauss. 



In the description of this figure, only those parts mentioned in the text are noted, although 

 the section shows very distinctly many other structures. 



At the convex border of the figure is the spinal cord, deeply stained, with the bulb at the 

 first bend above ; in front of the chord is the notochord, with the forming intervertebral disks 

 deeply stained ; the uppermost part of the figure is the head-cavity ; the midbrain is in the 

 central part of the head-cavity, above the nearly vertical projection continuous with the bulb, 

 which forms its floor ; the hindbrain and the cerebellum lie behind the midbrain ; the dien- 

 cephalon is in front ; beneath the snout is the tongue, with the heart below ; the liver is 

 below the heart, separated from it by the diaphragm ; the bronchia and lungs lie behind the 

 heart and liver ; the stomach and intestines lie below the liver, and a loop of small intestine 

 extends into the umbilical cord, which lies in front of the intestines ; the testis lies behind the 

 intestines, close to the notochord. 



FIG. 6. Sagittal section of a pig-embryo of ^ inch (12 mm.), x 5 (picro-carmin). Strauss. 



This figure shows an earlier stage of development than is shown in Fig. 5. Below the 

 head-cavity is the mandible the tongue has not appeared ; 'the diaphragm has not appeared, 

 and the thorax and abdomen form a single cavity. 



