STANDING. 589 



cells in the anterior horns or in the motor nuclei of the medulla oblongata also 

 give rise to atrophy of the muscles connected with them. Spinal paralysis and 

 acute bulbar palsy (paralysis of the medulla oblongata) thus have an acute onset, 

 while progressive muscular atrophy and progressive bulbar paralysis pursue a 

 chronic course. Under these conditions the muscles and their nerves become thin 

 and wasted. The muscles exhibit many nuclei, their contractile substance is 

 partly in a state of fatty degeneration, and later disappears altogether. The 

 intramuscular connective tissue is increased, often also the interstitial fat. Ac- 

 cording to Charcot, the central nerve-cells are also the trophic centers for the 

 nerves arising from them and for the related muscles. According to Friedreich, 

 however, progressive muscular atrophy is a primary disease of the muscles, a 

 primary interstitial myositis resulting in atrophy and degeneration, the central 

 nervous system becoming involved in the degenerative processes only secondarily ; 

 just as after amputation of an extremity corresponding parts of the spinal cord 

 degenerate secondarily. 



Finally, mention should be made of pseudo-hypertrophy or lipomatous mus- 

 cular atrophy, in which the muscle-fibers are completely atrophied, in association 

 with an abundant development of fat between the fibers, without, however, 

 degeneration of the nerves or the spinal cord. The muscular substance may also 

 undergo amyloid degeneration, the amyloid substance penetrating and infiltrating 

 the tissue. At times atrophic muscles exhibit a deep brownish-red color, probably 

 due to alteration of the muscle-pigment. Muscles constantly compelled to per- 

 form a large amount of work, such as the heart-muscle, the bladder, the intestine, 

 undergo hypertrophy. If the mechanism of the skeleton becomes altered, for 

 example as a result of rigidity of a number of joints, the muscles adapt them- 

 selves more or less completely to the altered mechanical conditions by changes 

 in their growth, expenditure of energy, and manner of movement. 



SPECIAL MOVEMENTS. 

 STANDING. 



Standing is the vertical position of equilibrium of the body, secured 

 by muscular action, in which the line of gravitation that is a perpen- 

 dicular dropped from the center of gravity of the body strikes the ground 

 within the supporting area of the soles of both feet. Of the various posi- 

 tions, that of "standing erect" will be analyzed here. In this position, 

 muscular activity is exercised in two directions : ( i ) to fix the articulated 

 body into an inflexible column (to "stiffen"); and (2) in case of a 

 variation of the equilibrium to neutralize the disturbance by suitable 

 muscular contractions. 



The following muscular activities are observed in standing: 

 i. Fixation of the head on the vertebral column. The occiput may 

 move in various directions on the atlas, whose two concave articular 

 surfaces converge anteriorly. The act of nodding is the most readily 

 performed. As the center of gravity of the head lies in front of the 

 supporting points on the atlas, relaxation of the muscles, as in sleep or in 

 death, causes the chin to fall upon the chest. The strong muscles of the 

 neck, which pull from the spinal column upon the occiput, fix the head 

 on the vertebral column. 



In addition to the nodding movement directly forward, a similar movement 

 is also possible obliquely forward and to the side. Rotation of the head in the 

 articulations of the atlas is possible only to an inappreciable extent around the 

 sagittal axis, likewise around the vertical axis, the latter occurring only when 

 the head is flexed. No special muscular activity is necessary to prevent these 

 movements in standing. When the head is rotated to the side, the contralateral 

 vertebral artery is compressed in the vertebral sulcus, while that on the same 

 side is enabled to carry more blood. 



The chief rotatory movement of the head occurs about the vertical axis of 



