513 



January 16, 1862. 



Dr. WILLIAM ALLEN MILLER, Treasurer and Vice- 

 President, in the Chair. 



The following communications were read : 



I. "On the Development of Striped Muscular Fibre in Man, 

 Mammalia, and Birds." By J. LOCKHART CLARKE, Esq., 

 F.R.S. Received November 21, 1861. 



(Abstract.) 



In the domestic fowl, until the beginning of the fifth day of incu- 

 bation, the so-called voluntary muscular tissue consists only of a 

 crowded multitude of free nuclei imbedded in a finely granular blas- 

 tema ; the nuclei are round, oval, pyriform, and somewhat angular, 

 with granular contents. On the fifth and sixth days of incubation, 

 fibres become superadded under two forms, 1st, as processes extending 

 from the ends, or from the sides of nuclei ; 2nd, as narrow bands, 

 either uniformly delicate and pale, or bordered by darker outlines, 

 and containing nuclei at variable intervals. They are most numerous 

 near the surface of the layer, and probably belong, at least partly, 

 to the muscular layer of the skin. In every case their first stage of 

 development is conducted on one general plan, which consists in the 

 fibrillation of the blastema along the sides of nuclei, to which the 

 fibrillee so formed become adherent. Sometimes these fibrillae or 

 lateral fibres enclose a single nucleus with conical processes of blas- 

 tema, so that the object occasionally presents some resemblance to a 

 fusiform nucleated cell. More frequently, however, they enclose a 

 linear series of nuclei at variable distances from each other, but 

 cemented together by blastema, which sometimes assumes around 

 each a more or less definite shape. In the formation of the paler 

 fibres, however, a series of neighbouring nuclei may sometimes be 

 seen first to collect round themselves granular masses of a more or 

 less fusiform appearance, and then to coalesce with each other, in an 

 oblique or alternately imbricate way. Sometimes a series of the 

 nuclei themselves overlie each other in an imbricate form like a 



VOL. xi. 2 P 



