MUSCULAR MOTION. 



519 



variety. Such is the case with the ductus cho- 

 ledochus in Birds, and probably in Mammals, 

 and in the ureters and vasa deferentia. The 

 bronchial tubes may be mentioned under this 

 head as the best marked example of this ar- 

 rangement. The trachealis muscle consists evi- 

 dently and entirely of the unstriped fibres, and 

 the same may be traced down the bronchial 

 ramifications as far as the air-cells themselves, 

 though not into them. The distinctive charac- 

 ters of this form of muscle may here be une- 

 quivocally discerned, and if anatomists had 

 been better acquainted with them, there would 

 not have been room for those disputes regarding 

 the muscularity of the bronchial tubes which 

 have so long attracted the interest of practical 

 physicians. Recently, indeed, there has been 

 added to the satisfactory evidence of anatomy 

 the well proved fact that these fibres may be 

 excited to contraction by the galvanic stimulus.* 

 In the case of other glands it is still unknown 

 how far the muscular cout invests the ramifica- 

 tions of the duct ; it is most likely that it gra- 

 dually ceases a short way within the organ, 

 and at least it seems clear that no portion 

 of the secreting membrane itself is ever in- 

 vested by it. 



e. Of the distribution of the striped and 

 unstriped fibres in the animal kingdom. 

 The striped fibres have been found in all ver- 

 tebrated animals, and in Insects, Crustacea, 

 Cirropods, and Arachnida. Future researches 

 will probably discover them even more exten- 

 sively diffused. But in the lower animals, 

 especially when they are of small size, we find, 

 as formerly mentioned, that the distinctive cha- 

 racters of the two varieties begin to merge into 

 one another and be lost. The transverse stripes 

 grow irregular, not parallel, interrupted; a fibre 

 at one part will possess them, at another part 

 will be without them; and even the peculi- 

 arities of the unstriped fibres are sometimes no 

 longer to be met with in parts which are un- 

 doubtedly muscular, as the alimentary canal 

 of small insects. It is evident that here the 

 elementary fibres, if of their usual bulk, would 

 be greatly disproportioned to the requirements 

 of the case, and consequently even the minute 

 ultimate fibre seems to be reduced within 

 limits which remove from it those anatomical 

 characters by which alone we can positively 

 aver its existence. Considering, however, the 

 circumstances which have been already ad- 

 verted to in this article, as determining the size 

 of the elementary fibre in all animals, we 

 should not be justified in denying the same 

 ?uscular tissue to exist here which in the higher 

 and larger forms of life assumes the figure 

 and bulk of the elementary fibre ; and by the 

 same mode of reasoning it may be concluded, 

 that a tissue having the same properties as the 

 striped fibre, and indeed essentially identical 

 with that of which they consist, may possibly 

 be the effective agent to which are due those 

 wonderfully vivacious movements witnessed in 

 the bodies of many of the minutest infusoria, 

 where the best microscope can hardly do more 



* Dr. Williams, on Diseases of the Chest, last 

 edition, Appendix. 



than discern the organs thus put in motion. 

 And it seems far from an unphilosophical view 

 of the nature of ciliary motion, to refer it to 

 the contractions of a tissue not entirely dif- 

 ferent in kind from the muscular. The ele- 

 mentary fibres of muscle, diminutive though 

 they he, and hardly discernible with the eye, 

 are yet gross organs in comparison with those 

 which the microscope enables us to conceive 

 capable of being formed out of them, without 

 any necessary destruction or even injury of 

 their contractile power. 



f. Chemical constitution. There is little to 

 add on this subject to what will be found under 

 the head of FIBRINE. By the aid of the mi- 

 croscope, however, our knowledge has been 

 rendered somewhat more precise, as to the 

 chemical properties of the elementary struc- 

 tures existing in the fibres. If any substance 

 capable of dissolving fibrine (as liq. ammonias) 

 be added to the muscular fibre, this is seen to 

 swell, to lose more or less completely its trans- 

 verse and longitudinal markings, and to exhibit 

 at once those corpuscles or cytoblasts, which 

 before lay concealed among the sarcous ele- 

 ments. These corpuscles and the sarcolemma 

 are not affected, but the sarcous elements are 

 almost entirely taken up. But for however 

 long a time the fibre be exposed to the alka- 

 line menstruum, there will always remain a 

 kind of web, of extreme tenuity and trans- 

 parency, from which the sarcous elements ap- 

 pear to have been withdrawn. This may be 

 seen in a transverse section of a muscle that 

 has been thus treated, then washed and dried. 

 I have not been able to detect in it any sort of 

 structure.* 



( W. Bowman.) 



MUSCULAR MOTION. Under this 

 head it is intended to consider the contractility 

 of muscle, its source, the stimuli that excite 

 it, and the nature of the minute movements 

 occurring during the act of contraction. 



a. Of the contractility of muscle. This 

 subject having already been ably discussed in 

 this work (see CONTRACTILITY), I shall here 

 confine myself to such a brief statement as 

 may appear to be required by the advance of 

 knowledge since the publication of the article 

 in question. 



1 . Is it a property inherent in the muscular 

 fibre? Are we to believe in the ' vis insita of 

 Haller? The supporters of this opinion have 

 always been exposed to the objection that in 

 the cases of contraction adduced by them as 

 the effect of a topical or immediate stimulus, 

 the isolation of the muscle from all connexion 

 with nervous fibrils has not been demonstrated. 

 Moreover, what has generally been regarded as 

 their strongest ground, viz. the statement that 

 involuntary muscles are not capable of being 

 excited to contraction by irritation of their 

 nerves, has lately been shown by the numerous 



[* The principal facts relating to the morbid 

 states of Muscle will be found in the articles 

 HEART, Morbid States of, and HYPERTROPHY and 

 ATROPHY. An historical sketch of the subject 

 concludes the article MUSCULAR MOTION. ED.] 



