MUSCLE. 



517 



Fig. 299. 



* , I* 



View of the capillaries of mvscle (part of the latis- 

 simus dorsi of a mouse, where it consists of a sinyle 

 sheet of fibres}. 



a, a, termiual twig of the artery. 



b, b, terminal twigs of two neighbouring venous 

 branches, anastomosing, and carrying off blood 

 from the same capillary net-work c, c. 



e, an elementary fibre, to show the relative size 

 and direction of those to which the capillaries here 

 represented are distributed. 



particles are compressed and elongated, some- 

 times to a great extent, evidently by the nar- 

 rowness of the canal which contains them. 

 It may seem at first sight not doubtful that in 

 the living creature these elastic blood-discs are 

 similarly elongated in their passage through 

 the vessels of muscle, but the admirable re- 

 searches of Poiseuille will perhaps serve to 

 explain this appearance without our being 

 driven to suppose the presence of so formid- 

 able an obstacle to the capillary circulation 

 through these organs. It is more probable 

 that the contraction of the vessels and the com- 

 pression of the blood-discs occur, on some of 

 the contents of the vessels being permitted to 

 escape by the severing of the fragment for 

 microscopic examination. The coats of the 

 capillaries of muscle consist of a simple diapha- 

 nous membrane, in which a few irregular-shaped 

 cytoblasts occur at infrequent intervals. 



Of the nerves of muscle. The distribution 

 of the nerves through muscular structures has 

 always been a subject of great interest with 

 those who looked to this line of inquiry for 

 some clue to the explanation, either of that 

 wonderful active connexion subsisting between 

 them, or of the nature of the contractile act 

 itself. But though the anatomical results ac- 

 cruing from this inquiry are of a highly satis- 

 factory kind, considered in themselves alone, 



yet they cannot be said to have hitherto contri- 

 buted, in any great degree, to the elucidation of 

 these mysterious questions. The best mode of 

 inspecting the arrangement of the ultimate ner- 

 vous twigs, is to select a very thin muscle, (as 

 one of the abdominal muscles of any small 

 animal, or one of the muscles of the eye of a 

 small bird,) to steep it in weak acetic acid, and 

 then thin it out under the compressorium. The 

 primitive tubules of the nerve may then be 

 readily distinguished with a power of 100 to 

 200 linear. They separate from one another, at 

 first in sets, afterwards in twos, threes, or fours, 

 and if these be followed they will be found 

 ultimately separating from one another, form- 

 ing arches, and returning either to the same 

 bundle from which they set out or to some 

 neighbouring one (fig. 300). In this loop- 

 like course they accompany to some extent the 

 minute bloodvessels, but do not accurately 

 follow them in their last windings, since then- 

 distribution is in a different figure. They pass 

 among the fibres of the muscle, and touch the 

 sarcolemma as they pass; but as far as present 

 researches have informed us, they are entirely 

 precluded by this structure from all contact 

 with the contractile material, and from all im- 

 mediate intercourse with it. How then shall 

 we explain the transmission of the nervous in- 

 fluence to a material thus enclosed ? If it 

 were wise or safe to go a single step in advance 

 of pure observation on so abstruse a question, 

 we might suggest, resting on the seemingly 

 sure ground of exact anatomy, that this in- 

 fluence must be of a nature capable of ema- 

 nating beyond the limits of the organ which 

 furnishes it. But further than this, as to how, 

 or to what extent this influence may so emanate, 



Fig. 300. 



Loop-like termination of the nerves in voluntary muscle. 

 After Burdacli. 



or as to what may be its nature, it would, per- 

 haps, in the present state of knowledge, be 

 hardly warrantable even to speculate. 



d. Of the distribution of the striped and 

 unstriped fibre in the. body. The striped fibre 

 is met with in all the voluntary muscles, and 

 in a few involuntary, as the constrictors of the 



