284 Dr. Waller on some Tissues of the Animal Frame, 



fibres crossing in every direction, like straight lines or cylin- 

 ders, of an even outline and without any subdivisions: at the in- 

 ferior surface they are still more distinctly seen, from the greater 

 thickness of the epithelial covering and the absence of papillae : 

 and from the mode of arrangement they may be compared to 

 the threads of a piece of linen, or the beams of a raft. Thus 

 we generally find one layer of fibres arranged transversely in a 

 parallel direction, and with considerable intervals between 

 them. Below these, by varying the focus slightly, appear 

 other fibres cutting them at right angles, but otherwise ar- 

 ranged in a similar way. In this manner appear successive 

 layers of muscular fibres at different angles. In addition to 

 these layers is the genio-glossus proceeding from the convexity 

 of the lower jaw-bone, and composed of round fibres arranged 

 together like a bundle of reeds, gradually expanding in a 

 curved direction towards the anterior extremity of the tongue. 



For a long period all the muscular fibres of the tongue were 

 considered to be destitute of striae, and to belong to the fibres 

 of the second class, such as those which line the intestinal 

 tube. Such is the description still given of them by M. 

 Donne at page 1 IS, Cours de Micros. 



As the other muscles of the frog which are under the influ- 

 ence of the will are known to present the characteristic stria?, 

 it appeared to me a curious anomaly that the muscular fibres 

 of the tongue, which are equally voluntary, should be without 

 them. For that reason I was induced to examine the mus- 

 cular parts of the tongue of the toad, to ascertain whether the 

 like exception existed there: I found the striae to be as di- 

 stinctly marked as they are in any of the other voluntary mus- 

 cles of the body. I have since on various occasions succeeded 

 in observing them equally distinctly in the muscular fibres of 

 the frog's tongue. 



I will now mention what I have been able to observe with 

 respect to the presence or absence of these striae, as the sub- 

 ject may be deemed interesting from its bearing upon some of 

 the theories of muscular contraction. The characteristic 

 striae are always to be perceived upon the muscular fibre of 

 the toad's tongue ; but in order to detect them conveniently 

 (the tongue of this animal not being so expansive as that of 

 the frog), a few slight incisions may be made, which can be 

 done without injuring any large vessel. In the young animals 

 of this species we may frequently be able to draw aside, and 

 secure with a pin, a transparent, membrane-like cellular tis- 

 sue, in which an active circulation can be observed for a long 

 time, and the distinctive streaks of muscular fibre over its en- 

 tire surface likewise. After these membranes have been sub- 



