1863.] 669 



tions are situated, if the specimen be so prepared as to prevent 

 destruction of these most delicate fibres, and the refractive power of 

 the medium be such as to enable us to see them. 



I propose to present to the Royal Society next session a paper in 

 which I shall demonstrate the truth of the conclusions I have arrived 

 at ; but as my specimens are already prepared, and during the last 

 few months several drawings have been made, I hasten to give a 

 short statement of facts, in order that those who have been led to 

 conclusions opposed to my own may have an opportunity of studying 

 the very same muscle. 



The great width and refractive power of the large elementary 

 fibres of the pectoral of the common frog render it impossible to 

 follow for any great distance amongst them nerve-fibres of the 

 6Q Q OQ th of an inch = *000187"' in diameter; and I have there- 

 fore long been searching for a very thin voluntary muscle, with fine 

 fibres, which, like the bladder of the frog, could be examined with- 

 out the necessity of making thin sections, and thereby deranging the 

 relation of all the finest and most delicate structures. Such a muscle 

 I have found in the extensive mylo-hyoid of the little green tree-frog 

 (Hyla arborea). The elementary fibres of this muscle are scarcely 

 more than the 3-5^ th of an inch = '0036'" in diameter ; and as 

 there are but two layers, the fibres of which are at right angles to 

 each other, all the structures in the muscle can be demonstrated 

 most beautifully. The very long thin muscular fibres are not too 

 close for exact observation. The vessels can be readily injected.* 



These specimens have been prepared upon the same plan as 

 others, and are preserved in glycerine, which enables me to press 

 the thin muscle and separate the fibres further from each other, 

 while the finest fibres of the nerves are prevented, by the viscid 

 medium, from breaking or from being so compressed amongst the 

 other tissues as to be destroyed or rendered invisible. The muscle 



* The very thin and wide intercostal muscles of the Chameleon, after having 

 been soaked in glycerine, may be separated into two layers, external and internal 

 intercostals, in each of which the finest ramifications of the nerve-fibres may be 

 followed, and their relation to the sarcolemma demonstrated. The long ele- 

 mentary fibres of the thin tubular part of the tongue of the same animal are also 

 favourable for this investigation; but the Chameleon is only to be obtained occa- 

 sionally, and the muscle of the green tree-frog, above referred to, possesses many 

 advantages. 



