MR. SKEY ON MUSCULAR FIBRE. 379 
it would be interesting to ascertain the relation which subsists between the central 
filaments, supposing the fibre to possess them, and the transverse strise. 
I have never seen any appearance like that of filaments projecting from the inte- 
rior of the fibre at its extremity ; for although the exhibition of the tubular character 
may be rare, involving as it does many conditions, yet it is not unreasonable to ima- 
gine, that if the fibre were solid, the extremities of the central filaments would be 
occasionally as apparent, as those which are arranged on its external surface. 
5th. Analogy to other structures would enable us in some degree to comprehend 
the utility of the circular strise, supposing them to surround a tube which they pro- 
bably compress in certain states of its action. 
Are th o, filaments like the fibres which they compose tubular ? 
Up to a late period of my inquiries into this subject, I had only the ground of ana- 
logy to support the opinion of the tubular character of the filaments, but being 
engaged in examining the muscular coat of the trachea of a Horse, I was not a little 
gratified to observe the very apparently tubular composition of these threads, one of 
which, indeed, placed at right angles to the plane below it, exhibited its cavity to 
some distance within (Plate XVIII. fig. 2.). Indeed the filaments presented very much 
the aspect of miniature fibres, in which I could almost fancy I saw some traces of 
still minuter threads. This though speculative is, I think, not very improbable ; but 
of the tubular nature of these delicate threads, I have no doubt; they were distinctly 
perceptible to many observers. 
From the above I deduce, 
That the human muscular fibres of animal life possess an average diameter of -^y^-th 
of an inch. 
That they are surrounded by circular striae varying in thickness and in number. 
That the striae are actual ridges or elevations on the fibre, leaving depressions be- 
tween them, considerably smaller than the globules of the blood. 
That each fibre is divisible into bands or fibrillae, which, composed of many ulti- 
mate filaments are arranged in parallel longitudinal lines around the axis of the fibre, 
and that the partial separation of these fibrillae produces the occasional broken or 
interrupted appearance of the circular striae. 
That each band or fibrilia is subdivided into filaments, of which every fibre of -Hr-g-th 
of an inch diameter contains about 100. 
That the muscular filaments possess a diameter of about the third part of a globule 
of the blood, or - rg \- 6 0 th of an inch, and that they are tubular, and that these fila- 
ments are arranged longitudinally around the tube of the fibre, which finally contains 
a soluble gluten. 
The human fibre of animal life pervades the whole of the external muscles, and all 
internal muscles connected to any form of tendinous matter. This will include those 
of the tongue, palate, larynx, and pharynx, with some portion of the oesophagus pro- 
longed from it, and constituting an exception to this rule ; the muscles of the orbit 
3 D 
MDCCCXXXVII. 
