PROTOPLASMIC, AMCEBIC, AND OTHER MOVEMENTS 317 



the phenomena witnessed in moving muscular masses, voluntary and involuntary. In order to give it the semblance 

 of truth, it is necessary to assume that when a hmb is voluntarily folded or flexed, the flexor muscles forcibly drag 

 out or extend the corresponding extensor muscles, and that, conversely, when the limb is opened out or extended, 

 the extensor muscles forcibly drag out or extend the corresponding flexor muscles. Similar remarks are to be made 

 of the abductor and adductor, and of the pronator and supinator muscles. According to this theory, the flexor 

 and extensor muscles are constantly at war with each other ; they are inconsistently pitted against and opposed 

 to each other — the primary object in view, namely, the movements of the bones to which the muscles are attached 

 and the increase or diminution of the angles made by the bones, and on which voluntary movements mainly 

 depend, being quite lost sight of. As regards the involuntary muscles, the theory is still more unsatisfactory. If 

 the movements of the mammalian heart be taken in illustration, it assumes that the very thin and weak 

 auricles by their closure or contraction forcibly open and dilate the very thick and powerful ventricles. This is 

 an impossible task ; the ventricles, at the end of the systole, being a solid muscular mass. As a matter of fact, 

 and as I shall show further on, the ventricles open spontaneously and independently when the auricles close 

 or contract : conversely, the ventricles spontaneously close when the auricles spontaneously open. The two 

 movements are correlated, but the one does not depend upon or cause the other. In proof of this I may state 

 that in the living heart the ventricles open and close even when the auricles, and the blood which they contain, 

 are removed. 



The objections to the prevailing theory of muscular action become apparent in cases where two sets of 

 muscles (a longitudinal and a transverse or circular) are arranged at right angles to each other, as in the large 

 and small intestines, in certain arteries, &c. In such examples, according to the prevailing theory, the longitudinal 

 and circular muscles are opposed to each other and their movements are, of necessity, mutually destructive. This 

 dilemma is avoided by investing both sets of muscles with a double power, namely, a power of contracting, shorten- 

 ing, or closing the one instant, and of relaxing, elongating, or dilating the next. The double power is well seen in 

 the arterioles or smallest arteries with only an imperfect circular layer of muscle. In this case, as is well known, 

 the artery can, in virtue of muscular action alone, be either contracted, narrowed, and elongated, or distended, 

 widened, and shortened. When longitudinal and transverse muscles are arranged at right angles, as in the 

 intestine and larger arteries, they act consentaneously ; the sarcous elements of the one set elongating when 

 those of the other set contract, and vice versd. In no other way could the peculiar vermicular movements of the 

 gut and blood-vessels be economically produced. The arrangement here advocated largely dispenses with elas- 

 ticity as a factor in muscular movements ; muscles acting in two directions by the inherent vital powers of their 

 sarcous elements. 



These views were advocated by me as far back as 1872,^ and are fully illustrated by original dissections, 

 photographs, and careful drawings in Plates Ixxxiii., Ixxxiv., and Ixxxv., and also Plates xc%di. to ciii. (seven 

 plates hthographed by Messrs. West Newman, the reference to which must be given further on). 



In cases where elasticity forms a factor of movement in animals, elastic structures are, as a rule, provided. 

 Thus, there are elastic inter-vertebral cartilages for the spinal column to diffuse shock ; elastic membranes in the 

 wings of insects, birds, and bats to flex and recover the wings after being extended ; elastic ribs, cartilages, &c., 

 to assist in respiration ; elastic Kgaments to support the strain of heavy parts, as the ligamentum nuchm supporting 

 the head of the deer — other ligaments restraining and hmiting the movements in joints, &c. In these and other 

 cases special provisions are made for the employment of elastic structures and substances. One of the best examples 

 of elastic structures is afforded by the arteries, especially the aorta, the great blood-vessel of the body, which is 

 subjected to the constantly recurring impulses or shocks generated by the rhythmic contractions of the left ventricle 

 of the heart. It receives the successive discharges of blood from the left ventricle and distributes that fluid to all 

 parts of the body. The aorta is a remarkably elastic structure throughout. It is dilated mechanically by the 

 blood forcibly ejected from the left ventricle of the heart during the systole or closing of the ventricle, and in virtue 

 of its elasticity it recoils and narrows its cahbre during the diastole or opening of the ventricle. The aorta by its 

 recoil gives a second or sub-impulse to the blood, and so assists in the circulation and performs a double duty. It 

 receives and diffuses shock and is dilated in the fiist instance ; it is narrowed mechanically by recoil and equahses 

 and assists the flow of blood in the smaller arteries in the second instance. The dilatation of the aorta and the 

 larger arteries of the body with each successive beat of the heart produces the pulse. The pulse is not felt in the 

 smaller and smallest arteries. In these the blood current is largely regulated by the vaso-motor nerves and by 

 special muscles in the arteries themselves — the elastic properties of the vessels being greatiy reduced, and mainly 

 confined to the lining membrane of the arteries. In the smaller arteries there are two sets of muscles, a so-called 

 circular set winding round the arteries more or less spirally, and a longitudinal set running in the direction of the 

 1 "The Physiology of the Circulation in Plants, in the Lower Animals, and in Man." 



