TUB MUSCULAR SYSTEM. 249 



in Eolidina, and some Rotifera ("Ann. d. Sc. N.," 1843, p. 300, and pi. 

 11, fig. 12). I myself, in a larva of Chironomus (a dipterous insect), 

 noticed a single nerve-fibre, proceeding to the two muscular fasciculi of 

 the simple tarsus, bifurcate into two branches, which were implanted upon 

 the surface of the muscle, with somewhat expanded terminations. In 

 the Vertebrata, Miiller and Brlicke first described division of the nerves 

 in the orbital muscles of the Pike (J. Miiller, "Physiol.," 4th ed. vol. 1, 

 p. 524), and in Amphioxus, Quatrefages noticed conditions precisely like 

 those met with in the Invertebrata above mentioned. The observation 

 is easily confirmed, as respects the orbital muscles of the Pike, in which, 

 upon the teasing out of the fasciculus either of the fresh muscle as well 

 as after it had been treated with corrosive sublimate, and rendered trans- 

 parent by acetic acid, numerous divisions of the nerves are apparent. 

 They are nevertheless not nearly so frequent in this case, as in the Frog, 

 nor are the divisions more than bifid or trifid. Besides this, I was espe- 

 cially struck with the glaring contrast that was presented, to what is seen 

 in the Mammalia, in the enormous extent of space included in the dis- 

 tribution of the nerve-fibres; a distribution so extensive, that it is by no 

 means easy to find a single primitive fasciculus which has not a nerve- 

 fibre going to it; in many places even, the latter were seen in apposition 

 with a fasciculus throughout a great extent, and surrounding it with 

 loops, or with a variable number of spiral convolutions. A similar con- 

 dition was observed by R. Wagner in the orbital muscles of the Torpedo, 

 whilst in other muscles the nerves were very scantily supplied (" Gb'tt. 

 Nach.," Oct., 1851). In the Amphibia, divisions and free terminations 

 of the nerves have been described by Wagner. The former are remark- 

 ably beautiful and numerous. They commence in nerve-fibres, measur- 

 ing 0-004-0*006 of a line, in the smaller trunks and branches, and are 

 several times repeated, with a gradual diminution of the fibres, until 

 extremely minute filaments measuring 0'001-0'0015 of a line are 

 formed. The divisions are for the most part di- or tri-chotomous, more 

 rarely multiple; in one instance, however, Wagner noticed eight ramus- 

 culi. The ultimate filaments are pale, and have a simple contour line. 

 They never penetrate into the muscular fasciculus, but, after running a 

 short distance, are either applied obliquely or transversely to it, or proceed 

 for some distance in close contiguity and parallel with it; in either case, 

 becoming attenuated to a sharp point, and frequently as fine as a fibril 

 of connective tissue. All these conditions are best seen in the mylohyoi- 

 deus (Wagner), and above all, in a delicate cutaneous muscle of the 

 thorax, as was pointed out to me by Ecker, and in which the distribu- 

 tion of the nerves has recently been very accurately described by Reichert. 

 He observed in this case, as I had done in man, that only a small por- 

 tion of the muscle was well supplied with nerves, which were but spar- 

 ingly distributed to the other portions. The trunk of the nerve supply- 



