intercostals, as by the muscles of the extremities? Paralysis in these last only takes from the animal a means of communication with external objects; in the others it interrupts immediately both internal and external life. The nervous influence is only propagated from the superior to the inferior part, and never in an inverse direction. Cut a nerve in two, its inferior part when irritated will make the subjacent muscles contract; let them do what they will to excite the other, no contraction is produced in the superior muscles; so the spinal marrow divided transversely and pricked above and below, produces no sensible effect but in the second direction. The nervous influence never extends upward for motion, as it does for sensation. _Animal Contractility considered in the Muscles._ The muscles essentially destined to receive the cerebral influence by means of the nerves, have however an active part in their own contraction. It is necessary that they should be entire to exercise this property, and answer to the excitement of the brain. When any lesion affects their texture, and it is no longer the same as usual, the muscle remains immoveable or moves with irregularity, though it receives a regular nervous influx. The following are various circumstances relative to the muscle itself, which prevent or alter its contractions. 1st. An inflamed muscle does not contract; the blood which then infiltrates it and penetrates its fibres, their great excitement and the increase of its organic forces, do not permit it to obey the stimulus it receives. In angina, deglutition is as much interrupted by the inaction of the muscles, as by the inflammation of the mucous membrane. We know that the inflammation of the bladder is one cause of the retention of urine; that of the diaphragm renders respiration very painful, which the intercostals perform almost alone. 2d. Every thing which tends to weaken and relax the muscular texture, as external blows, bruises, contusions, infiltrations of serum in dropsical limbs, or distension from a subjacent tumour long continued, alters, changes the nature of, and can even annihilate animal contractility. 3d. Whenever the blood ceases to enter the muscles by the arteries, these organs remain immoveable. Steno has observed, and I have always seen, that in tying the aorta above its bifurcation which forms the internal iliacs, paralysis of the inferior extremities immediately comes on. We know that in the operation for aneurism, a numbness more or less considerable almost always follows the ligature of the artery. This numbness continues until the anastomoses supply the place of the artery which no longer brings any fluid. The internal motion created in the muscle by the entrance of the blood, is then a condition essential to muscular contraction. Thus the habitual motion imparted to all the other organs and especially to the brain, maintains their excitement and their life.