Lateral ventricle

“ From Johannes Adelphus, Mundini de omnibus humani corporis interioribus menbris Anathomia, Strassburg, 1513. The diagram shows the two lateral ventricles and the ‘central’ ventricle. By a printer’s error the letters c and d are transposed. The arteria adorti is the aorta, the arteria venalis the pulmonary vein, the vena chilis the vena cava, and the vena arterialis the pulmonary artery. The auricles are ignored, as is frequently the case in works of the period, and the pulmonary veins are represented as opening directly into the ventricles. ”

“ This being a median section, the ventricles of the fore- (fb) , mid- (mb) , and hindbrain (hb) are seen as large cavities, while the cerebral hemispheres (ch) appear nearly solid, only a small portion of a lateral ventricle showing. The paraphysis (epi) is cut a little to one side of the middle and so does not show its connection with the brain. At the base of the brain the infundibulum (in) is seen as an elongated [331] cavity whose ventral wall is in close contact with a group of small, darkly staining alveoli (p) , the pituitary body. ”

“ Its cavity is known as the third ventricle. Just craniad of the [343] ’tween-brain, in the median line, is a deep fissure, showing that here in reality is the termination of the original tube, the further extension craniad being due to the pushing forward of the lateral outgrowths, or cerebral hemispheres, which extend in ventral view a considerable distance further craniad. The hemispheres lie also caudad, laterad, and dorsad of the midbrain and ’tween-brain, so that these parts are almost enveloped by the hemispheres. ”

“ Every animal that has lungs has therefore two ventricles to its heart, one right, another left; and wherever there is a right, there also is there a left ventricle; but the contrary of this does not hold good: where there is a left there is not always a right ventricle. The left ventricle I call that which is distinct in office, not in place from the other, that one namely which distributes the blood to the body at large, not to the lungs only. Hence the left ventricle seems to form the principal part of the heart ”

“ It sometimes (though rarely) happens, that, with an increase of strength and bulk in its muscular structure, the left ventricle suffers a diminution of capacity in its cavity. In a case reported by Laënnec, the left ventricle was an inch and a half thick at its broadest, and an inch thick at its thinnest part ”

“ The blood ought to push against the semilunar valves with a force not less than 1/2 - 2/3 of the force of the contraction of the ventricle, because this is about the relative height of the first secondary elevation with regard to the primary wave, which is due to the contraction of the ventricle. ”

“ The auriculo-ventricular valves differ in structure in the two ventricles. That of the left ventricle has only two flaps, and is therefore often spoken of as the bicuspid or mitral valve. Both these flaps are membranous, and together they completely surround the exit from the auricle into the ventricle. The edges of the valve are bound down to the parietes of the heart by numerous branching tendinous threads, the chordae tendineae, which often take their origin from pillar-like muscles arising from the walls of the heart, the so-called musculi papillares. ”

“ The ventricle, in correspondence with it being the main pumping apparatus, has its walls much thickened by the development of muscular trabeculae which, in the lower forms separated by wide spaces in which most of the blood is contained, become in the Teleostomes so enlarged as to give the wall a compact character, the spaces being reduced to small scattered openings on its inner surface. In the Dipnoans the ventricle, like the atrium, is incompletely divided into a right and left ventricle. ”

“ It seems to me that the left side of the heart has a great deal more work to do than the right, for the left has to force the blood into the main artery, and all over the body, to the toes, the fingers, the brain: but the right ventricle only has to force it through the lungs that are close by, touch the heart, and it is a short route. ”

“ For neither are the conduits small, nor the contractions few in number, but frequent, and always in some certain proportion, whether it be a third or a sixth, or an eighth, to the total capacity of the ventricles, so that a like proportion of blood must be expelled, and a like proportion received with each stroke of the heart, the capacity of the ventricle contracted always bearing a certain relation to the capacity of the ventricle when dilated. ”

“ It is believed by most physiologists that the essential factor in the production of heart block is an interference in the conduction of [141] impulses from the auricles to the ventricles through the band of tissue known as the auriculoventricular bundle.
Fig. 47.—Electrocardiogram showing delayed conduction (lengthening of P-R interval) . These P-R intervals are quite regular. When irregular there is apt to be extrasystole of ventricle or occasional blocking of impulse going to ventricle. ”

“ Pressure in the ventricle must exceed that in the arteries before the semilunar valves will open and the blood can be driven out, just as the auriculo-ventricular valves remain closed until the pressure in the auricles exceeds that in the ventricles.
The heart beat is caused by the twisting of the heart upon its axis during contraction of the muscle. Normally it beats rhythmically and regularly, whatever a person does, at a rate of about seventy-two contractions to the minute in the adult. ”

“ As soon as the beat of the ventricles is over and the ventricular muscle relaxes, the blood which has accumulated in the auricles presses the intake valve open and blood begins to flow through it directly into the ventricle. ”

“ But no one need remain in doubt of the fact, for if the ventricle be pierced the blood will be seen to be forcibly projected outwards upon each motion or pulsation when the heart is tense.
These things, therefore, happen together or at the same instant: the tension of the hearty the pulse of its apex, which is felt externally by its striking against the chest, the thickening of its parietes, and the forcible expulsion of the blood it contains by the constriction of its ventricles. ”

“ When one listens over the chest to a heart when extrasystoles are occurring, one suddenly hears a weak beat [140] which has taken place rather too early after the previous systole to be strong enough to effect the opening of the aortic valves. Consequently there is no pulse, the blood does not move, and that beat is lost to the circulation. Moreover, when the next regular stimulus comes from the s-a node it finds the ventricle in a refractory condition, having just ceased a contraction, and it is not until the next sinus impulse that the ventricle responds normally. ”