Zooloykul Society. 393 



disposed transversely, in which respect it may be seen with the 

 naked eye to differ from the oesophageal muscular sheath of mam- 

 mals, in a few fishes the striated muscular fascicles invested the 

 entire length of the gullet, and extended some distance on the sto- 

 mach in others, as in the pike and bull-head. In the barbel some of 

 these fascicles were found on the gullet or termination of the pha- 

 rynx opposite to the posterior border of the gill-cover. In Fishes 

 tiie striated muscular fasciculi of the gullet appear, from the mea- 

 surements now given, to be much smaller than the fasciculi of the 

 muscles of the body ; and a like difference, though to a much smaller 

 degree, often exists in mammals. 



" In the heart of the smaller species of the lower Vertebrata di- 

 stinct muscular fibres are often not to be found, the structure being- 

 less distinct than in the heart of many mammals ; generally composed 

 of bands or fillets not easily separable from each other, and com- 

 monly about 5o\kJ^^ "^^ ^^ ^"^^^ broad. These fillets are seldom 

 clearly streaked transversely ; they are irregularly and most minutely 

 granulated, without the longitudinal arrangement of the granules 

 so plainly visible in the beaded primitive fibrils of the heart of 

 Mammalia. In short, the known points of resemblance between 

 the muscular fibre of the heart of mammals and that of voluntary 

 muscle are generally wanting in the structure of the heart of the 

 smaller species of the lower Vertebrata, for the latter is more nearly 

 allied to the muscular tissue of organic life as it exists in other 

 parts . 



" In some of the voluntary muscles of many of the smaller Mam- 

 malia and Birds, as the common mouse and FriugillidcE, the existence 

 of a sheath around the fibres appears to be questionable ; and in the 

 heart of such animtds the fibres are remarkably indistinct. In the 

 common water-vole I noticed a very clear appearance of primitive 

 fibrils, yet these seemed to be nowhere collected into fascicles. In 

 the great pectoral muscle of various small birds, as the common swift, 

 the transverse streaks are very indistinct, and often difficult to be 

 seen, although they are very plain in the muscles of the leg ; yet in 

 this bird the former muscle is highly developed, and almost con- 

 stanth' in action, while the latter are but small and little used. It 

 will be recollected that the above remarks apply only to particular 

 muscles, and are not to be considered as at all invalidating the ad- 

 mirable demonstration of the sarcolemma in many muscles by Prof. 

 Schwann and Mr. Bowman, and the parallel observations of Dr. Jones 

 Quain and Mr. W. J. E. Wilson*. As before observed, the fibres 

 of the heart of Mammalia seem to have no intervening cellular (fila- 

 mentous) tissue ; this tissue, however, is easily observed in the heart 

 of many lower vertebrate animals ; and I have very recently seen 

 minute wavy filaments, having all the characters of cellular tissue, 

 in the heart of the bear, and of some other mammals which had died 

 in confinement." 



The term fibre, as used in this paper, corresponds to the primitive 

 fasciculus of Fontana, Miiller, and Bowmanf. As in the heart there 



* See Phil. Trans, part ii. 1840, p. 47.1. f Loc. cit. p. 458. 



Ann. £f Mag. N. Hist. Vol xi. 2 D 



