438 GENERAL ANATOMY. 



out their extent; those which line the urinary and genital pro- 

 longation of the same membrane, form the bladder, the sper- 

 matic vesicles, and the uterus; those of the pulmonary pro- 

 longations of this membrane which form the bundles of the 

 trachia and bronchse. The sphincters, which are found at the 

 orifices of the alimentary canal and the urinary and genital 

 passages, may be regarded as intermediate to the two classes 

 of muscles. Nearly the same is the case with respect to the 

 texture, and more especially the functions, of the muscles of 

 the skeleton, which are subservient to digestion, respiration, 

 generation, and the urinary excretion. There is not, then, 

 any very marked distinction between the two classes of mus- 

 cles. 



703. The muscles in question are placed in the interior; 

 some situated immediately under the internal tegument, and 

 in particular, the heart, is situated very deeply and distant 

 from the two surfaces, of which it is entirely independent. 



The volume of these muscles is very inconsiderable when 

 compared with that of the exterior muscles; they all form the 

 parietes of canals and of reservoirs. 



704. These muscles are disposed in layers or in bundles 

 crossing each other. 



Throughout the whole extent of the alimentary canal, there 

 are circular or annular fibres, and longitudinal fibres, each 

 forming a distinct plane, more or less complete and thick. 



In the reservoirs, as well as in the heart, the fibres are dis- 

 posed in layers and bundles which cross each other obliquely, 

 they have an arched form, the extremities of which are fixed 

 to the sides of the aperture of the organ. The bundles of 

 fibres in these organs cross each other, and are united in the 

 manner of plexuses. This arrangement is less marked in the 

 alimentary canal, where the muscular layers cross each other 

 at right angles. 



The muscular fibre of the interior muscles is of a grayish 

 white in most of them, and red in the heart only. This fibre 

 differs in no other respect from that of the exterior muscles. 

 The uterus alone in this respect presents a well-marked differ 

 ence, and characters entirely peculiar. 



