518 



MUSCLE. 



pharynx and the muscular coat of the oeso- 

 phagus, and the heart. In the oesophagus it 

 appears to be mingled with the other variety to 

 a somewhat uncertain extent. In some speci- 

 mens from the human subject I have been un- 

 able to detect any striped fibres in the lower 

 half of that tube, either in the circular or 

 longitudinal layer, but in other examples they 

 have been traceable to within an inch of the 

 stomach. Among the lower animals consider- 

 able differences occur, as has been well pointed 

 out by Mr. Gulliver,* who observes that in 

 general " the muscular fibre of animal life 

 (striped) extended further towards the stomach 

 in the outer than in the inner layer of the ceso- 

 phageal muscular sheath." In several animals 

 this gentleman found the striped fibres even on 

 the stomach (as in the Rabbit, Lepus cuniculus, 

 Linn., the Sheep, Ovis (tries, Desm., the Sloth 

 Bear, Ursus lubiatm, Blainv.) while in many 

 others he met with them to within a very short 

 distance of that cavity. Dr. Todd has also 

 shewn them to me on the glandular pouch at 

 the cardiac extremity of the stomach in the 

 Dormouse. It is still unknown in what manner 

 the two varieties of fibre are arranged at this 

 point of junction, some supposing that they 

 are simply intermixed, others that they pass 

 into one another by imperceptible gradations. 

 The former of these views is that which appears 

 most consonant with my own observations. 

 Mr. Skey considersf that the fibres of the heart 

 " possess a somewhat compound character of 

 texture," and this opinion seems highly pro- 

 bable. They possess, it is true, the transverse 

 stripes indicative of an arrangement of particles 

 in parallel series, but there is frequently a want 

 of that uniformity and precision in this appear- 

 ance which so remarkably characterize voluntary 

 muscle. The cross lines are apt to be broken 

 and interrupted, and are sometimes difficult to 

 discover at all. This condition is well repre- 

 sented by Mr. Skey in fig. 5 of his second plate. 

 In some of the smaller and lower animals the 

 particles never form transverse stripes. These 

 fibres, as explained by him, are smaller than 

 the average diameter of the voluntary muscles 

 of the same subject by two-thirds, and in most 

 parts of the heart they are not aggregated in 

 parallel sets, but twine and change their relative 

 position. Striped fibres have been found in the 

 iris, in the small muscles of the ear, and in 

 those muscular fasciculi that surround the ure- 

 thra immediately in front of the prostate. They 

 are also found in the sphincters of the anus and 

 vagina. 



The unstriped fibre is met with in the ali- 

 mentary canal from the middle of the oeso- 

 phagus to the rectum, and constitutes the double 

 layer investing that tube. It also forms the 

 muscular coat of the bladder and that of the 

 uterus. The dartos owes its contractility to the 

 presence of fibres of this variety, which, in con- 

 sequence of the abundant admixture of areolar 



* Proceedings of the Zoological Society of Lon- 

 don, No. 81, Sept. 1839. 



t Phil. Transactions, 1837, p. 381. 



tissue, has not hitherto been clearly recognized ^ 

 but it may be detected by the addition of acetic 

 acid, which, by bringing into view the peculiar 

 corpuscles it contains, distinguishes it from both 

 the white and yellow fibrous elements of the 

 areolar tissue. But even without this chemical 

 test, to which some may object, it is possible 

 to discover this form of muscular fibre in the 

 dartos, by the characteristic appearances which 

 have been already attributed to it. Since satis- 

 fying myself of the real existence of this fibre 

 in the dartos, I have on many occasions de- 

 tected a very decisive peristaltic action advan- 

 cing from one side of the scrotum to the other, 

 and continued for a considerable period, yet of 

 a kind which it was impossible to refer, with 

 any degree of probability, to the cremaster. 

 In one case particularly, occurring in the prac- 

 tice of Mr. Fergusson, where the tunica dartos 

 was much hypertrophied, in connection with 

 an old stricture of the urethra, we observed this 

 peristaltic contraction of a very vigorous de- 

 scription. The fibres which have been de- 

 scribed as peculiar to the dartos seem to be 

 nothing more than a certain modification of the 

 areolar tissue in that region. In the corpora 

 cavernosa penis of the horse there is a large 

 quantity of this kind of fibre, as may be ascer- 

 tained by microscopic examination, although 

 Professor Muller* seems indisposed to consider 

 it really muscular. He states that " viewed in 

 the microscope these fibres do not present any 

 resemblance to muscular fibres," but my own 

 examinations of them have not confirmed this 

 statement. They appear to me to have all the 

 characteristics of this variety, and by acetic 

 acid are seen to contain a great number of cor- 

 puscles. Moreover they appear to consist che- 

 mically of tibrine. Professor Muller has failed 

 in exciting contraction in them in the living 

 horse, but this is not a conclusive fact as to 

 their nature, for it may be and probably is the 

 case that they do not act unless stretched by the 

 erection of the organ. In the quiescent condi- 

 tion of the part they may be considered to be 

 in a contracted state, like the muscular coat of 

 an empty intestine, and so would naturally 

 appear to be unaffected by the stimulus of 

 galvanism. The erection of the penis seems 

 with great probability to be attributable to 

 pressure exercised on the superficial veins of 

 the organ by a continuation of a structure ana- 

 logous to the dartos, and certainly containing 

 the unstriped muscle, which is continued over 

 the base of the penis under the skin. The 

 erection of the nipple also occurs, on any me- 

 chanical irritation, with a motion so very much 

 resembling the peristaltic action of muscular 

 fibres, that I have little doubt such would be 

 found, constituting a layer, under the skin in that 

 region. And it may be matter of inquiry how 

 far the general contractility of the skin is de- 

 pendent on a diffusion of this tissue, in small 

 quantities, throughout its areolar structure. The 

 excretory ducts of all the larger glands appear 

 to possess a covering of fibre belonging to this 



* Physiology, by Baly, second edition, p. 250. 



