324 DESIGN IN NATURE 



PLATE LXXXIV {continued) 



Fl«. 4. — Photograph of a frozen section of the human heart where the individual has died during the systole of the organ, that 

 is, when the ventricles were strongly contracted and the ventricular cavities obliterated ; the auricles being relaxed and distended 

 to their utmost, a. Cavity of right auricle ; h, cavity of left auricle ; c, thickness of wall of right auricle when relaxed ; d, e, thick- 

 ness of wall of left auricle when relaxed ; /, thickness of wall of left ventricle when the ventricle is fully contracted and the 

 ventricular cavity obliterated ; g, /i, great vessels cut into. 



Shows the comparative thickness of the walls of the ventricles and auricles during systole, and how it is impossible for the 

 thin auricles to force their contained blood into the ventricles, which, in systole, form solid muscular masses. The obvious in- 

 ference is that the ventricles open spontaneously when the auricles close. The auricles do not forcibly dilate the ventricles, 

 neither do the ventricles forcibly dilate the auricles. The movements of the auricles and ventricles are co-ordinated but they are 

 independent ; the ventricles opening by centrifugal movements when the auricles close by centripetal movements, and vice versa. 

 The ventricles are invested with a double power, whereby they can alternately open and close, and the same is true of the auricles. 

 A similar arrangement obtains in the hollow viscera (stomach, bladder, &c.) with sphincters. 



All the muscular fibres of the ventricles and auricles move simultaneously and harmoniously in the opening and closing move- 

 ments. The opening centrifugal movements and the closing centripetal movements of the ventricles are shown in Pig. 3 (the 

 Author, 1872). 



Fig. 5. — Diagram showing the centripetal and centrifugal movements of the left ventricle during systole, when the ventricular 

 cavity is obliterated, and during diastole, when the ventricular cavity is fully opened, as seen in cross section of the ventricle. The 

 muscular fibres are in a state of activity during both the closing and opening movements. There is, however, a brief interval 

 between the opening and closing movements when the ventricle is at rest. There is also a period of rest for the sarcous elements, 

 which greatly extends the period of the inactivity of the ventricle as a whole, a, Zone of rest for the left ventricle ; b, contracted 

 zone when the left ventrical cavity is obliterated by a strong centripetal movement of the muscular fibres, as indicated by the tour 

 long arrows ; c, relaxed zone when the left ventricular cavity is fully opened up by a more feeble centrifugal movement of the 

 fibres, as indicated by the four short arrows. The centripetal and centrifugal movements are spontaneous and independent of each 

 other. They are also vital in their nature (the Author, 1867). 



Fig. 6. — Muscles of the iris of the eye. a, Transverse or circular muscular fibres ; b, longitudinal or radiating muscular fibres. 

 These are arranged at right angles to each other. They are of the plain, unstriped type, and have for their object the increase and 

 diminution of the pupil or aperture in the centre of the iris through which the light passes into the interior of the eye. The 

 transverse or circular fibres have been regarded as forming a sjjhincter, and the longitudinal radiating fibres a dilator, to the iris ; 

 these acting at different times and alternately. The circular and longitudinal fibres are said to be opposed to, and pitted against, 

 each other, after the manner of supposed antagonist muscles. This is an erroneous view. As a matter of fact, the so-called 

 sphincter and dilator muscular fibres are co-ordinated, and act harmoniously and together ; both taking part in the opening and 

 closing movements of the iris. The movements of the muscular fibres are centrifugal and centripetal in character, as in small 

 blood-vessels, the hollow viscera, and the voluntary muscles when these produce the movements of flexion and extension, of 

 abduction and adduction, of pronation and supination, &c. 



Some are of opinion that the longitudinal fibres are sparse or non-existent, and that when present they are striated, as in the 

 bird and otter. If this view be adopted it follows that the circular fibres must of themselves be equal to increasing and diminish- 

 ing the aperture of the pupil, and that they are consequently endowed with a double power, which enables them to increase or 

 diminish the size of the pupil at pleasure (after Iwanoff). 



PLATE LXXXV 



Plate Ixxxv. shows how the small arteries are furnished with transverse or circular and longitudinal or straight 

 unstriped muscular fibres arranged in two layers with nuclei interspersed ; how the unstriped muscular fibres are 

 ribbon-shaped and flat, and display rod-hke nuclei in their interior ; how the nuclei reappear in young striped muscle 

 with faint transverse markings ; how in the adult heart the transverse marldngs are pronounced, the involuntary 

 and voluntary muscles having not a little in common, structurally and functionally. In particular the Plate shows 

 how the ventricles of the mammalian heart open and close, the cavities of the ventricles being quite obhterated 

 during the systole ; how the muscular fibres of the left ventricle are arranged spirally in two sets, which enter and 

 leave the apex at opposite points, and so produce a symmetrical result, which, curiously enough, finds its exact 

 counterpart in certain shells (Plate xiii., Fig. 1, G) and in double spiral nebula3 (Plate viii.). The last is a most 

 unexpected occurrence, and has much significance, as indicating the prevalence of laws which have symmetry and 

 spiral movements for their objects. 



/M ■^"'L^'T-f"' ^'"''." ^'■*®-^?' ''.°"^'^*i"g °f transverse and longitudinal unstriped muscular fibres branching into two smaller ones 

 (/;), which split up into capillaries (c and d) displaying nuclear elements. Magnified 225 diameters 

 B. Nuclei (ff, (I, a) of unstriped involuntary muscles, magnified 350 diameters. 

 ■^ 0. Flat spindle-shaped involuntary muscles, showing rod-like nuclei {a, n, a) ■ the central specimen being treated with acetic 

 dkmeterT according to some investigators, display faint traces of transverse and longitudinal cleavage. Magnified 350 



D, E. Similar fibres with well-marked nuclei (o, (t). 



F Elementary fibres from pectoral muscle of fcetal calf two and a half months old, showing corpuscles (a, a), magnified 300 

 diameters This preparation affords a Imk between the involuntary and voluntary muscular fibres structurally and unctionally. 

 MagnVd^^rSet^rMBowl^^ '^"-^^ °' ' '-'''"' '' '" ^" ""^''^ ^'^'^ °^ development, showing central row of corpuLles. 



H. Striped mvoluntary muscle of the heart. The cardiac muscle is peculiar in this : it is involuntary and yet its substance 

 displays we 1-marked transverse and longitudinal cleavages. It runs the involuntary and voluntary muscle into each othei ^nd 

 affords proof that both kmds of muscles belong to a common stock, and functionally resemble each other ' 



