Part 100

9. Turn the duodenum toward the left and note the pancreas, a light red, elongated organ which stretches along the greater curvature of the stomach and thence between the two lines of the duodenal U to its bottom.

10. The spleen, parallel to the gastric portion of the pancreas. It is deep red (darker than the pancreas and not so brown as the liver) and is held against the great curvature of the stomach by a part of the great omentum.

11. The kidneys, close against the dorsal body wall and in contact with the caudal part of the liver.

12. The bladder, in the median line at the caudal end of the cavity, held in place by the suspensory ligament, which passes to the midventral line, and by the lateral ligaments.

13. The mesenteric glands, large grayish-red glands one to four centimeters long, more numerous in the mesocolon.

14. In the female, lying against the ventral surface of the rectum, the uterus. It divides into two horns which diverge. Near the end of each horn the ovary.

15. The peritoneum. Study and understand the description of it (p. 218). Dissect some of it free from the body wall. (Trace the folds by aid of a diagram and model.)

B. In the thoracic cavity:

1. The lungs. Each is divided into lobes, three on the left, four on the right. The caudal right lobe pushes the mediastium toward the left and thus lies in a pocket dorsocaudad of the heart and dorsad of the vena cava inferior.

2. The pleuræ. Each pleura is a membrane like the peritoneum. It covers the diaphragm and the thoracic walls and is reflected onto the lungs. Hence it is divided into costal and pulmonary portions. Read the description (p. 217) and trace their connection. Each pleura forms a closed sac.

3. The mediastinal septum or median vertical portion formed by the apposition of the medial walls of the two pleural sacs. It divides the thorax into halves.

4. In the mediastinum or space between the halves of the mediastinal septum are seen--

a. Ventrally (i.e., in the anterior mediastinum), blood-vessels and fat, and craniad the pink thymus gland. Read the description of the thymus (p. 254, and Fig. 107).

b. Dorsally (i.e., in the posterior mediastinum) the trachea (best seen craniad), the œsophagus (best seen caudad), and the aorta.

c. In the middle (reckoning in a dorsoventral line) (i.e., in the middle mediastinum) the heart, with the inferior vena cava approaching it from the rear. Prick into the mediastinum and inflate it. Remove the thoracic wall opposite the one already removed, so as to stretch the mediastinum and show it more clearly. Expose the trachea beneath the caudal end of the sternomastoidei. Note the thyroid gland (Fig. 96, 6, p. 229). Insert a blowpipe without injury to the thyroid, and inflate the lungs. Cut the sternum at its caudal end and turn it craniad, cutting the mediastinal septum and noting its double character.

Dissect the mediastinal septum from the thymus so as to expose this organ.

d. The pericardium, a relatively thick-walled sac, within which the heart lies. The pericardium is covered by the mediastinal septum on each side, but not dorsally and ventrally. Dissect the mediastinal septum from the pericardium. Prick and inflate the pericardium. Open it and expose the heart.

DISSECTION OF THE ALIMENTARY CANAL.

Study and verify the descriptions of the organs as they are dissected.

I. Salivary glands (p. 223).

1. Keep the mouth open by a cork between the teeth. Find the papillæ upon which open the sublingual and submaxillary ducts (pp. 223 and 224); remove the mucosa and enlarge the opening and insert a black bristle into either duct. Trace the duct by the bristle as far as possible on the floor of the mouth.

2. Find the white ridge formed on the cheek by the parotid duct (p. 223). It is opposite the molar tooth, and at its cranial end the opening of the duct is seen. Enlarge the opening and insert a black bristle as far as possible.

3. Remove the skin and the skin-muscles from the side of the face, beginning at the caudal end and working craniad. At the cranial border of the carotid on the ventral side look carefully for the parotid duct with the bristle in it. The duct is then easily traced by the removal of the skin and muscles. Study the parotid gland (Fig. 131, 10, p. 322).

4. Remove the facial vein (Fig. 131, b and c) and lymphatic gland (Fig. 131, 12) covering the submaxillary gland (Fig. 131, 11) and clean its outer surface. Raise it and find the submaxillary duct leaving its inner surface. Reflect the digastric and mylohyoid muscles and trace the duct to the oral mucosa. The remainder of its course is shown by the bristle on the inside of the mouth.

5. The sublingual gland is uncovered in dissecting the submaxillary. Its duct is seen by the side of the submaxillary. It may be pricked near the gland and a bristle passed to its opening.

6. The infraorbital gland. Expose it by removal of the zygomatic arch and masseter muscle. Find its duct by dissecting apart the lobules at its ventral end. Prick the duct and insert a bristle to find its inner opening.

7. The molar gland. Find it by raising the orbicularis oris of the lower lip. By raising its ventral border and dissecting between it and the mucosa the ducts may be found and perhaps pricked and bristles inserted.

II. The mouth-cavity. Study the general description (p. 221); the lips and the cheek. Then remove the masseter muscle and the caudal part of the zygoma. Cut through the mandible between the first premolar and the canine tooth. Then disarticulate the mandible, cut the cheek and also the mylohyoid muscle and oral mucosa parallel to the medial border of the mandible, and remove the mandible with the parts thus left attached to it. The organs in the mouth-cavity are thus left exposed and should be studied. To demonstrate the incisive ducts (p. 222) pass a bristle into them.