350 MUSCLE?. 



sent a perfect similitude of structure every where. The most 

 numerous class, as well as that in which they are of the greatest 

 magnitude, are the muscles of voluntary motion : they are placed 

 between the skeleton and the integuments, and constitute the 

 principal bulk of the extremities, and also afford a thick fleshy 

 covering to the trunk. The second class is contained within 

 the large cavities of the skeleton, and forms a portion of the 

 structure of the circulatory, of the digestive, and of the urinary 

 organs ; and produces the principal internal motions of the ani- 

 mal economy. 



Every muscle is surrounded by an envelope of cellular sub- 

 stance, called its sheath, (Membrana Musculorum Communis*) 

 which at different points of the body exhibits various degrees of 

 condensation. In the muscles of voluntary motion these sheaths 

 are formed by partitions, going from the aponeurotic expansions 

 just beneath the skin, to the periosteum, and are the prolonga- 

 tions which induced Bichat to consider the periosteum, as the 

 centre of the desmoid system. These sheaths in some cases pre- 

 serve to a considerable extent the ligamentous appearance, but 

 generally cellular substance predominates in them. Upon their 

 existence is founded the great variety of views and descriptions 

 which the later anatomists have taken of the fascia? of the hu- 

 man body, some choosing to describe them in one way and some 

 in another. The sheaths of the second class of muscles are com- 

 posed of a much finer and looser coat of cellular substance than 

 those of the first, and are commonly described as lamina? or tu- 

 nics to the organs to which they respectively belong. In every 

 ease, however, from the internal face of these sheaths a great 

 many partitions pass off, which penetrate the body or thickness 

 of the muscle, and divide and subdivide it into fasciculi, and into 

 fibres, even to their most minute condition. These partitions be- 

 come thinner the more they are multiplied. 



Many of the muscles are subdivided by fissures, into several 

 large portions called Fasciculi, or Lacerti. These vary very 

 much in size, and in their distinctness from each other. Some 

 are so large and so widely separated as to appear like distinct 

 muscles; such, for example, are the biceps of the arm and of the 

 thigh, the deltoid, the columnar carneas of the heart, and several 

 others. But the greater part of the fasciculi are strictly parallel 



* Haller, Element. Physiol. torn. i. 



