Part 7

Make a drawing of the ventral side of the skull.

3. Make a drawing of the bones of the skull viewed from the posterior end, showing the occipital condyle at each side of the foramen magnum, ex-occipitals, basi-occipital, supra-occipital, pro-otics, columella, and quadrate.

4. Remove the skin from the lower jaw and make out the bones surrounding the original Meckel's cartilage, viz., the mento-meckelian, dentary, and articular.

Make a drawing of the lower jaw.

Nervous System.

A. The Central Nervous System.

The Brain.

Carefully remove the fronto-parietals so as to expose the brain, and note the following parts:--

(a) The olfactory lobes, forming the most anterior portion of the brain, united together in the middle line. Anteriorly the olfactory nerves are given off.

(b) The cerebral hemispheres, a pair of smooth elongated bodies.

(c) The thalamencephalon, lying immediately behind the cerebral hemispheres. It is covered by the choroid plexus, a thick vascular membrane, and gives rise dorsally to the stalk of the pineal body.

(d) The optic lobes, a pair of oval bodies.

(e) The cerebellum, a narrow transverse band immediately behind the optic lobes.

(f) The medulla oblongata behind the cerebellum. It gradually tapers towards its posterior end, where it is continuous with the spinal cord. On its roof the pia mater forms a very vascular choroid plexus.

Make a sketch of the brain.

Seventh Day. (Revision.)

With a second specimen revise the second, third, and fourth days' work, paying particular attention to the vascular system.

Eighth Day.

=Nervous System= (continued).

B. The Peripheral Nervous System.

1. The Spinal Nerves.

Remove the abdominal viscera carefully so as to expose the spinal nerves which are seen as white cords on each side of the vertebral column as follows:--

(a) The first or hypoglossal nerve arising between the 1st and 2nd vertebræ. It runs forwards on the under surface of the head beneath the mylo-hyoid muscle and supplies the tongue. It was noted in the third day's work.

(b) The second and third nerves unite immediately after escaping from the spinal cord to form the brachial plexus, which supplies the muscles of the shoulder, and then extends along the arm.

(c) The fourth, fifth, and sixth nerves are small and supply the muscles and the skin of the body wall.

(d) The seventh, eighth, and ninth nerves run obliquely backwards, the eighth and ninth uniting to form the sciatic plexus, which gives rise to the large sciatic nerve which extends along the thigh, and down the leg. The sciatic plexus also receives a branch from the seventh nerve.

(e) The tenth or coccygeal nerve, which escapes through a small aperture in the side of the urostyle, and is distributed to the walls of the cloaca and urinary bladder. It is connected by a branch with the sciatic nerve. This nerve is frequently small or absent in the Platana.

2. The Sympathetic Nervous System.