280 GENERAL ANATOMY OF MUSCLES. 



that is, have no cavity in their interior, and vary much in their 

 size. The second class consists of those placed in the interior 

 of the body, and which effect the movements requisite in the 

 various processes of nutrition and generation. These are not 

 under the control of the will, and are called the muscles of 

 organic life, muscles of the life of nutrition, involuntary muscles, 

 etc. They are generally membraniform, and assist in forming 

 the hollow organs, as in the heart, digestive canal, uterus and 

 bladder. With the exception of those of the heart, the fibres 

 of this class of muscles are of a pale color, and some entirely 

 colorless. A few of the muscles of animal life, as those of the 

 ears and some of those of the face, are likewise faintly colored, 

 and are considered by Isenflam,* as existing even in the adult 

 in a state of rudimental development, as their color and func- 

 tions are found much more fully manifested in some quadru- 

 peds.! 



The muscles in the inferior grades of animals appear to exist 

 in a rudimental condition, and become more and more nume- 

 rous, and of a color more and more red generally, as we 

 advance upwards from the zero point of the animal scale. In 

 the development of the human foetus they seem to undergo 

 analogous changes. 



They present themselves during the three first months of 

 foetal life, as gelatinous or viscous masses, very slightly tinged 

 with yellow, and with thin tendons, according to Isenflam, 



* Anatomische Untersuchungen, by H. F. Isenflam, Professor at the Uni- 

 versity of Dorpat. 



f This physiological division of the muscles into two classes, after Bichat, is 

 eminently useful to the student, in enabling him to simplify and generalize his 

 studies of the muscular system ; one class is not, however, wholly separate 

 from the other. Between, is interposed another subdivision of muscles, called 

 the Respiratory of Sir C. Bell, which with the muscles of the pharynx and 

 oesophagus, might be considered as a third or mixed class of muscles, as they 

 execute certain motions involuntarily and unconsciously to the individual, and 

 yet are under the influence of the will to perform motions for other purposes or 

 to execute the same motions more rapidly or more slowly. Thus, for instance, 

 the muscles of respiration which carry on the process of breathing during sleep, 

 produce involuntary sneezing, coughing and crying; and when placed under 

 the influence of the will are made to elicit the voice, etc. P. 



