Part 105

10. The vertebral artery (p. 291). Trace it to the foramen transversarium of the sixth cervical vertebra. Then with bone-forceps follow it to the atlas and into the atlantal foramen. Add this to your diagram of the subclavian.

11. The basilar artery (p. 291) and the other arteries of the brain (p. 289) are best studied on a preparation, similar to that shown in Fig. 121. To obtain such a preparation it is only necessary to remove the brain (for directions, see p. 462) of a specimen in which the arteries have been injected.

(12. Veins of the brain and dura mater (p. 324). These can be worked out only with much difficulty, except on specimens injected with gelatine. The skull must be chipped away and the veins followed without destroying them.)

13. Trace the pulmonary veins (p. 315) (filled with red injection) and the pulmonary artery (p. 280).

IV. Vessels in the abdominal cavity.

1. Open the abdominal cavity; find the superior mesenteric vein (p. 326, and Fig. 132) in the duodenal mesentery near the border of the pancreas. Inject this in both directions with white starch and then dissect the portal vein and its tributaries without injuring any of the structures in the abdomen (p. 326, and Fig. 132).

2. Follow the inferior vena cava (p. 325) from the heart to the diaphragm and then follow it to its tributaries in the abdominal cavity.

3. Dissect the branches of the abdominal aorta (p. 301) and of the inferior vena cava (Fig. 126). Make diagrams of the vessels dissected and review as far as necessary the viscera concerned.

V. The external iliac and its branches (vessels of the hind limbs) (pp. 309 and 329, and Figs. 127, 128, and 163).

Follow the branches of the external iliac arteries and the corresponding veins in the same manner as the vessels of the arm were traced, cutting the muscles only so far as absolutely necessary. Make diagrams of the vessels dissected.

Make a diagram (a) of the arterial system as a whole; (b) of the venous system as a whole.

THE LYMPHATIC SYSTEM (p. 330).

It will hardly be found practicable to have each student make a dissection of the lymphatic system, and such parts of it as are to be studied may best be shown on a specimen prepared for demonstration purposes.

The thoracic duct and the receptaculum chyli may be demonstrated by the following well-known method: A lean cat is fed with milk about two hours before killing it. An egg may be beaten up with the milk to advantage. Kill the cat with chloroform, and inject the arteries with colored starch through the femoral, in the usual way. The thoracic duct, the receptaculum chyli, and the lymphatics leading to the receptaculum chyli will be colored white by the milk, and can therefore be easily followed. For this purpose the abdomen should be opened, and the left side of the thorax removed, as in the dissection of the blood-vessels. The thoracic duct will be found at the left side of the aorta and may then be traced in both directions.

For a more complete study of the lymphatics they should be injected. This is done as follows: Make a glass canula with a small point, and leave the point sharp. Connect this to the syringe by means of a rubber tube. Use a saturated solution of soluble Prussian blue as injecting fluid. Employ a freshly killed animal.

For injecting the lymphatics of the limbs, make with some pointed instrument, as the tracer, a small hole in one of the pads on the sole of the foot. Introduce the point of the canula into this opening and inject the fluid. This will pass into the spaces in the connective tissue of the pad, which will swell up, and the colored fluid will pass from the connective-tissue spaces into the lymphatics. Pressure must be maintained with the syringe for a considerable time,--fifteen minutes to a half-hour for a good injection of the main trunks of the lymphatics of the limbs. The movement of the fluid should be facilitated by pressing and manipulating the limb at the same time with the hand,--in such a way as will tend to drive the fluid proximad.

The lymphatics of the head may be injected in a similar manner, the canula being introduced into the upper and lower lip, or into the bare surface at the end of the nose.

The internal lymphatic vessels may be injected by injecting the lymphatic glands with which they are connected. This may conveniently be done as follows: Draw out to a fine point the tip of an ordinary pipette or medicine-dropper. The point should be fine, but should taper rapidly in a conical fashion, so that when the point is inserted the part of the glass tube behind it will close up the opening.

Fill the pipette with soluble Prussian blue; insert the point into the gland, and inject the fluid slowly. The lymphatic vessels passing from the glands will be filled. By injecting thus the large lymphatic gland (“pancreas Aselli”) in the mesentery, the abdominal lymphatics, the receptaculum chyli, and the thoracic duct may be injected.

By using thin gelatine colored with Prussian blue as an injecting fluid permanent preparations may be obtained; of course the process of injection is then less simple, and should be looked up in some manual of methods.

NERVOUS SYSTEM.

I. THE SPINAL CORD (p. 335).

Use the specimen on which the muscles were dissected. (Or if the peripheral nerves are not to be dissected on the specimen used for the blood-vessels, that may be employed.)

Make a longitudinal dorsal median incision of the skin, between the back of the head and root of the tail. Reflect the skin for one or two inches on each side of the incision and cut away the muscles covering the neural arches of the vertebræ from the third cervical to the seventh or eighth thoracic inclusive.

Remove with bone-forceps the neural arch of one of the last cervical vertebræ and find the spinal nerve emerging from the intervertebral foramen. Isolate the nerve for a short distance, then proceed craniad, removing the neural arches on one side and isolating the nerves until the third has been uncovered. The ganglion of the second nerve should be sought among the muscles on the dorsal surface between the atlas and axis, and after it has been isolated the arch of the axis may be removed. (The nerve may be found beneath the clavotrapezius and traced to the ganglion.)

The ganglion of the second nerve should be isolated in or near the atlantal foramen, the muscles to which it passes turned aside, and the arch of the atlas removed. Having thus uncovered the first two or more spinal ganglia, proceed caudad, removing the vertebral arches, until the whole cord and its nerves are exposed. Then--

1. Study the cord, enlargements, filum terminale, etc. (p. 334, and Figs. 133 and 136).

2. Slit open and reflect the dura mater (p. 337) for an inch or two.