APPARATUS OF MOTION. 37 



points, motion of such points results when the muscular axis 

 is shortened. 



Muscles are divided into the striated (when the tubular 

 contents of each sheath are transversely divided into disks) 

 and the non-striated (when such division is absent). The 

 muscles are striated in Salpa and certain Polyzoa; Crusta- 

 cea, Arachnida, Insecta (with whom it is seen in both volun- 

 tary and involuntary muscles); and Vertebrata, with whom 

 it is confined to the voluntary muscles and heart. They 

 are non-striated in Radiata, Entozoa, and Annelida; Lamel- 

 libranchiata generally, Gasteropoda, Cephalopoda, and in 

 the majority of the involuntary muscles of Vertebrata. 



Muscles are white in Invertebrata,* Pisces, Batrachia, and 

 Reptilia. Exception, Salmo (salmon), Acipenser (sturgeon), 

 Squalus (shark), where they arc red. Constantly red in 

 Aves and Mammalia, excepting pectoral muscles of certain 

 grauivorous birds, as Perdix (partridge), Phasianas (pheas- 

 ant), Gallus (common fowl). This change of color is asserted 

 to be a result of fatty degeneration of muscular fibre, from 

 want of use, a view, in a measure, confirmed by the leg 

 muscles of Struthio (ostrich), which, ordinarily red, become 

 white when the animal is for some time confined. (Quekett.) 



Descriptions of special muscles. Adductor muscles of bi- 

 valve molluscs, pectoral muscle of birds. Diaphragm of 

 mammals, abdominal muscles of reptiles and mammals; 

 cremaster muscle; panniculus carnosus (platysma myoides); 

 muscles of external ear. Muscles peculiarly developed in 

 man are glutei and stern o-cleido-mastoideus. 



CILIARY ACTION. Due to the presence of cilia or sper- 

 matic filament. 



Cilia. These are minute processes (homogeneous fila- 

 ments), placed in connection with a basement membrane, 

 and endowed with a constant vibratile motion. 



In Vertebrata, cilia are attached to epithelial membrane; 

 but in other animals, and in certain embryos, they clothe the 

 peripheral surface of organism. They are seen in all ani- 



* See Appendix. 



