Part 6

8. Stimulation of the second parietal convolution, above and a little behind the extremity of the Sylvian fissure, causes opening of the eye and adduction of the ear on the opposite side, or, if a very strong current, on both sides.

9. Strong stimulation of the posterior part of the first and second parietal convolutions causes tonic convulsions.

10. Currents through the posterior parts of the third and fourth parietal convolutions gives similar convulsions with violent trembling of the trunk and members.

In the =Dog’s Brain= localization is easily made by reference to the crucial fissure which passes outward, right and left, at right angles with the longitudinal fissure about the junction of its anterior with its middle third. Also by four parietal convolutions which run backward from near the crucial fissure, parallel with the longitudinal fissure. They are counted from without inward. Fritsch, Hitzig and Ferrier have mapped out the following motor areas:

1. The convolution in front of the outer end of the crucial sulcus controls the muscles of the neck.

2. The bend of the same convolution backward, opposite the outer extremity of the crucial sulcus, controls the extensors and adductors of the fore limb.

3. The convolution just behind the outer end of the crucial sulcus controls the muscles which flex and rotate the fore limb.

4. The same convolution behind the middle of the crucial fissure controls the movements of the hind limb.

5. The second convolution back of the crucial fissure controls the muscles of the face.

6. The anterior part of the internal (4th) parietal convolution, just back of the crucial fissure, controls the lateral switching movements of the tail.

7. The posterior angle of the first post-crucial convolution causes retraction and abduction of the fore limb.

8. The outer end of the first post-crucial convolution, directly behind the outer end of the sulcus, causes raising of the shoulder and extension of the fore limb.

9. The anterior end of the third parietal convolution (the second from the longitudinal fissure) controls closure of the eyelids, the rolling of the eyeball upward, and narrowing of the pupil.

10. Stimulation of the anterior end of the second parietal convolution causes partial opening of the mouth with retraction and elevation of its angle.

11. Stimulation of the point of union of the first and second parietal convolutions anteriorly causes opening of the mouth with protrusion and retraction of the tongue.

12. Stimulation of the median part of the second parietal convolution, causes retraction and elevation of the angle of the mouth.

13. Stimulation of the convolution directly in front of the outer end of the crucial sulcus causes dilatation of the eyelids and pupil while the eyes and head are turned toward the opposite side.

14. Stimulation of the convolution behind the crucial fissure causes contraction of the muscles of the perineum.

15. Stimulation of the convolution in front of the crucial fissure, on its anterior and sloping portion, causes movements of the pharynx and larynx (swallowing).

16. Stimulation of motor areas of the cortex, by scraping, irritation, or disease tends to produce spasmodic contractions of certain groups of muscles (Jacksonian Epilepsy). Strong stimulation may cause general epileptiform spasms, which are at first tonic, then clonic. One such seizure strongly predisposes to a second. If, during an attack, the cortical centres presiding over a special group of muscles were sliced off, such muscles relaxed, though the general spasms in the other muscles continued.

Localizations of Spinal Lesions.

Being at once a conductor between the brain and nerves, and a reflex nerve centre, we must consider both rôles in seeking to locate lesions from symptoms. In passing from the nerves to and from the sensorium both sensory and motor currents cross so that one side of the brain presides over the other side of trunk and limbs. This crossing of the motor fibres takes place in the medulla oblongata, while that of the sensory fibres occurs in the spinal cord close in front of the nerve from which they have entered.

=Cross-Section of one lateral half of the spinal cord= therefore causes motor paralysis and rise of temperature of the whole of that side of the body posterior to the lesion, while it induces sensory paralysis and cooling on the opposite side of the body up to the same point. A very limited sensory paralysis on the same side occurs corresponding to the few sensory fibres passing outward obliquely through the portion injured by the cross-section.

=A vertical section of the cord separating the one lateral half from the other= does not necessarily affect the motor currents, while it produces a limited anæsthesia on each side in the area of distribution of the nerves, the sensory fibres of which crossed in the seat of the lesion.

=Transverse section of the superior columns= causes hyperæsthesia and lack of coördination.

=Transverse section of inferior columns=, or of the inferior horn of gray matter, if close behind the medulla, causes no motor paralysis, but if farther back induces motor paralysis on the same side of the body.

=Transverse section of the cervical lateral columns= causes motor paralysis of the lateral walls of the chest (respiratory tract). If the section is made in the dorsal or lumbar region it is the same as lesion of the superior columns.

Among =reflex centres= in the cord the following may be named: