omotion, as those of the organs of
sense, which constitute their ideas.

This last class of motion is the subject of the following pages; which,
though conscious of their many imperfections, I hope may give some pleasure
to the patient reader, and contribute something to the knowledge and to the
cure of diseases.

* * * * *

SECT. II.

EXPLANATIONS AND DEFINITIONS.

I. _Outline of the animal economy._--II. 1. _Of the sensorium._ 2. _Of
the brain and nervous medulla._ 3. _A nerve._ 4. _A muscular fibre._ 5.
_The immediate organs of sense._ 6. _The external organs of sense._ 7.
_An idea or sensual motion._ 8. _Perception._ 9. _Sensation._ 10.
_Recollection and suggestion._ 11. _Habit, causation, association,
catenation._ 12. _Reflex ideas._ 13. _Stimulus defined._

* * * * *

As some explanations and definitions will be necessary in the
prosecution of the work, the reader is troubled with them in this
place, and is intreated to keep them in his mind as he proceeds, and to
take them for granted, till an apt opportunity occurs to evince their
truth; to which I shall premise a very short outline of the animal
economy.

* * * * *

I.--1. The nervous system has its origin from the brain, and is distributed
to every part of the body. Those nerves, which serve the senses,
principally arise from that part of the brain, which is lodged in the head;
and those, which serve the purposes of muscular motion, principally arise
from that part of the brain, which is lodged in the neck and back, and
which is erroneously called the spinal marrow. The ultimate fibrils of
these nerves terminate in the immediate organs of sense and muscular
fibres, and if a ligature be put on any part of their passage from the head
or spine, all motion and perception cease in the parts beneath the
ligature.

2. The longitudinal muscular fibres compose the locomotive muscles, whose
contractions move the bones of the limbs and trunk, to which their
extremities are attached. The annular or spiral muscular fibres compose the
vascular muscles, which constitute the intestinal canal, the arteries,
veins, glands, and absorbent vessels.

3. The immediate organs of sense, as the retina of the eye, probably
consist of moving fibrils, with a power of contraction similar to that of
the larger muscles above described.