BY DR. KLEIN. 7-") 



rest of the muscular fibres enter the mucosa, and end in ten- 

 dinous bundles of equal diameter, which again unite with the 

 mesh work of the mucosa. 



Arrangement and Division of Muscular Fibres. 

 They are grouped into bundles by septa of connective tissue, 

 which in general contain numerous amoeboid cells, and a net- 

 work of ordinaiy branched cells. From these septa thinner 

 lamellae spring, which are interposed between the individual 

 bundles. In a mature foetus a cross section of muscular bun- 

 dles, e.g., of the tongue, palate, or eyelids, shows that they are 

 intersected by a beautiful network of nucleated branched cells, 

 in such a way that each mesh is occupied by a single fibre. In 

 general, striated muscles do not divide : there are, however, 

 situations in which muscular fibres are seen to divide dicho- 

 tomously or dendritically. The best example is to be found in 

 the cardiac muscular fibres, of which a repeated dichotomous 

 division is characteristic, as also their union with one another 

 so as to form a network. In the tongue of mammalia, the 

 muscular fibres often divide before ending in tendons ; but in 

 that of the frog the divisions occur much more frequently. 

 Both in recent preparations, and in sections made after hard- 

 ening, muscular fibres are seen which branch dendritically, as 

 they ascend towards the dorsal mucous membrane, the ulti- 

 mate branches being so small that they contain only a few 

 fibrils, which finally end in connective tissue fibres. 



Examination of Muscular Fibre in Polarized Light. 

 We assume the reader to be acquainted with the action of a 

 Nicol's prism, contenting ourselves with stating that the polari- 

 zation microscope is an ordinary microscope, in which one 

 Nicol is placed above the eye-piece or ocular (i. e. between the 

 eye-glass and the observer's eye), and a second between the 

 object and mirror. The upper Nicol is usually of one piece 

 with the ocular. The prism is so fixed that it can be rotated, 

 and that the axis of rotation is contained in its principal plane. 

 The degree of rotation is measured by a graduated circle. 

 The lower Nicol is surrounded by a condensing lens, and can 

 (in Hartnack's microscope) be "fitted into the tube which 

 ordinarily contains the diaphragm or condensor. In looking 

 through such a microscope, it is seen that the illumination ot 

 the field varies according to the relative position of the two 

 prisms ; so that, in rotating the upper one (which is called the 

 analyzer), it is darkened and lightened twice in each complete 

 rotation. The positions of greatest obscurity arc those in 

 which the principal planes of the two Nicols are at right angles 

 to each other of greatest luminousness, those in which these 

 planes are coincident. When the microscope is^used with the 

 Nicol in the first-mentioned position, the object is said to be 

 observed between crossed Nicols. 



