that act. Inosite, creatin, creatinin, and urea, are the products of muscular waste. It may be objected that the considerable shortening which a muscle undergoes could not be due to the amount of loss of material which one could suppose possible. Draper justly regards the experiment of placing muscle under water, to show that no change of bulk occurs during contraction, as most imperfect and inconclusive-as no calculation is made for the increased heat which would expand the water, or no provision for the removal of waste. The analogies of fibrillation and muscular contraction have been mentioned 122.

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Rigor Mortis is the cadaveric contraction which occurs between somatic and molecular death. It is regarded by Weber as due to elasticity, which, he thinks, was prevented from coming into play by contractility during life. Brücke states that it is but the fibrillation of the muscle-fibrin, and thus identical with coagulation of the blood. Others regard it as the last vital manifestation, and after its departure all irritability is lost and putrefaction ensues. Brown-Séquard, by injecting defibrinated arterial blood, removed the rigidity from the limb of an executed criminal 4 hours after it had set in, and kept up the irritability of its muscle for 41 hours, until the opposite limb began to putrefy. By cutting off the supply of arterial blood, stiffness similar to rigor mortis may be produced in living animals. Rigor mor-. tis usually commences about 4 hours after death, but has begun within 10 minutes, or has been delayed 7 hours. The earlier it begins and the more powerful it is, the shorter it lasts; whereas late and feeble contraction may endure for many days. It affects paralyzed muscles, unless much wasted. Involuntary muscles also exhibit it; thus the condition of the heart termed "concentric hypertrophy" is but a post mortem contraction, and the uterus has often expelled the foetus by the same action, when the mother has died undelivered.

After death by lightning, sudden injury, typhus, glanders, and other septic poisons, and some other causes, it either occurs so soon and in so trifling a degree as not to be perceived, or does not take place at all. It usually begins in the jaw and neck, and proceeds to the upper and lower extremities, from above downwards, departing in the same order.

The muscular force of the human body is utilized and increased by the frequent adoption of the lever. There are three kinds of this mechanical power-1st, where the fulcrum is intermediate, and the power and resistance at the ends. Of this kind there are not many examples. We have here represented one which is often

1st Order.- Rising on Tiptoe. 2nd Order.- Opening the mouth. incorrectly described as of the second order. In rising on tip-toe, the ankle is the fulcrum, the gastrocnemius the power, and the ground the resistance. Other examples are afforded when we erect ourselves after the trunk is bent forwards, the hip being the fulcrum, the hamstrings the power, the weight of the body the resistance; and in the nodding of the head backwards and forwards at the occipito-atlantoid joint. The 2nd order is best exemplified in the act of opening the mouth by the action of the digastric, which is the power, the tem

poro-maxillary articulation being the fulcrum, and the resistance the temporal, which is intermediate. The

3rd order is by far

the most frequently used. We have selected the wellknown example of the biceps, which is the power intermediate, the elbow being the fulcrum,

3rd Order.-Flexing the Forearm. and the hand, with any body grasped in it, the resistance. The deltoid, brachialis anticus, rectus femoris, temporal, and many other muscles, act with the aid of this kind of lever, as the greatest velocity is thus acquired, although with some loss of power. Sir C. Bell, in his charming book on "The Hand," says: The same interchange of power for velocity which takes place in the arm, adapts a man's hand and fingers to a thousand acts requiring quick or lively motions. The fingers of a lady at the pianoforte, or of a compositor with his types, are instances of the advantages gained by this sacrifice of force for velocity of movements.'

The power is usually placed very near the fulcrum, so that in the case we have sketched, if the biceps contracts one inch, the hand will traverse the space of a foot, but through each inch with only of the muscular force-a power which would bring all to rest if exerted in opposition.

The following attitudes and motions afford examples of associated muscular actions.

Standing in the erect posture is, as we have before stated, an attitude peculiar to man. The weight of the body is transmitted through many joints, and a line dropped through the centre of gravity must fall within the base of support-an invariable law of stability. In some instances the attitude is preserved more easily by

rapidly changing the centre of gravity-thus, the drunken man is less liable to fall if he runs than if he tries to walk slowly.

Walking is performed by flexing the knee and extending the ankle of one leg, which is thus raised from the ground; the weight is then thrown and the body inclined towards the opposite limb, which, by acting on the ball of the big toe, rises it from the ground, and transfers it to the limb which was first moved.

Running is accomplished by similar, but more rapid movements, the body being also constantly bent forwards. In leaping, both legs are raised at once from the ground.

QUESTIONS FOR EXAMINATION.

JUNIOR.

1. What varieties of motion are presented in plants and animals?

2. Describe the structure, distribution, and uses of white fibrous tissue, and the points in which it differs from the yellow.

3. Sketch the histology of the articular and membraniform varieties of cartilages.

4. Describe the arrangement of the bones in the most movable and the most immovable kinds of articulation.

5. Enumerate the notions of the older writers on the structure of bone, and describe what you have seen under the microscope. 6. What are the uses of bones, and why are the long ones hollow?

7. Explain how bones grow.

8. Describe the phenomena of muscular contraction and of the rigidity which occurs post mortem.

9. What are the orders of levers? Give an example of each.

SENIOR.

1. Describe ciliary motion, stating in what particulars it agrees with and differs from muscular contractility.

2. What synonymes have been applied to areolar tissue? With what other tissue is it associated, and in what situations do their respective amounts vary?

3. Give a precis of Prof. Redfern's researches on abnormal nutrition of cartilages.

4. What are the components of bone, and how may each be demonstrated?

5. Do the relative proportions of salts and gelatin vary with age, or with the hardness of bone?

6. From what other microscopic object could you predict the size of the lacunæ of any animal ?

7. Mention a few of the proportions which exist between the weights of the bones of animals.

8. Sketch the minute anatomy of voluntary muscle, and contrast its structure and properties with those of the two other varieties.

9. What are the stimuli to contraction, and which of them has influence longest after death?

VOICE AND SPEECH.

In man, voice is more perfect than in any other animal; and speech, expressing thoughts and feelings, is his special prerogative.

The Larynx is shown to be the organ of voice by that faculty being lost if the air be allowed to escape before passing through it, as we see in persons on whom we have performed tracheotomy; by the aphonia which results from injury of the vocal cords or inferior laryngeal nerves; and also by sounds being produced by blowing through the larynx, removed after death. The organ is made up of the following structures: 4 true cartilages-thyroid, cricoid, and 2 arytenoid; and 7 false or fibro-cartilages-the epiglottis, 2 cuneiform, 2 cornicula, and 2 corpora triticea, which are jointed by many ligaments, the elasticity of which increases the vocal vibrations, and moved by several muscles we shall afterwards allude to. In a physiological point of view the two openings of the larynx, the glottis and the rima glottidis, are the most important. The former lies behind the epiglottis, and between two mucous folds which pass from it backwards and inwards to the arytenoid