504 MOBILITY OF THE VERTEBR/E. 



and interossei chiefly undergo atrophy. Atrophy and degeneration of the muscles are followed 

 by shortening ami thinning of the bones to which the muscles are attached. 



Section and paralysis of the motor nerves cause palsy of the muscle, thus rendering them 

 inactive, and they ultimately degenerate. Atrophy also occurs after inflammation or softening 

 of the multipolar nerve-cells in the anterior horn of the grey matter of the spinal cord, or the 

 motor nutfci (facial, spinal accessory, and hypoglossal of Stilling in the medulla oblongata), in 

 the muscles connected with these parts. Rapid atrophy takes place in certain forms of spinal 

 paralysis and in acute bulbar paralysis (paralysis of the medulla oblongata), and in a chronic 

 form in progressive muscular atrophy and progressive bulbar paralysis. The muscles and their 

 nerves become small and soft. The muscles show many nuclei, the sarcous substance becomes 

 fatty, and ultimately disappears. According to Charcot, these areas are at the same time the 

 trophic centres for the nerves proceeding from them, as well as for the muscles belonging to 

 them. According to Friedreich, the primary lesion in progressive muscular atrophy is in the 

 muscles, and is due to a primary interstitial inflammation of the muscle, resulting in atrophy 

 and degenerative changes, while the nerve-centres are affected secondarily, just as after amputa- 

 tion of a limb, the corresponding part of the spinal cord degenerates. 



In pseudo-hypertrophic muscular atrophy the muscular fibres atrophy completely, with 

 copious development of fat and connective-tissue between the fibres, without the nerves or spinal 

 cord undergoing degeneration. The muscular substance may also undergo amyloid or wax-like 

 degeneration, whereby the amyloid substance infiltrates the tissue ( 249, VI.). Sometimes 

 atrophic muscles have a deep brown colour, due to a change of the haemoglobin of the muscle. 

 When muscles are much used they hypertrophy, as the heart in certain cases of valvular lesion 

 or obstruction ( 40), the bladder, and intestine. [In true hypertrophy there is an increased 

 number or increase in the size of its tissue elements, throughout the entire tissue or organ, 

 without any deposit of a foreign body. Perhaps, in hypertrophy of the bladder, the thickened 

 muscular coat not only serves to overcome resistance, but it offers greater resistance to bursting 

 under the increased intra-vesical pressure. Mere enlargement is not hypertrophy, for this may 

 be brought about by foreign elements. In atrophy there is a diminution in size or bulk, even 

 when the blood-stream is kept up, the decrease being due to pressure. An atrophied organ may 

 be even enlarged, as seen in pseudo-hypertrophic paralysis, where the muscles are larger, owing 

 to the interstitial growth of fatty and connective-tissue, while the true muscular tissue is 

 diminished and truly atrophied.] 



308. STANDING. The act of standing is accomplished by muscular action, 

 and is the vertical position of equilibrium of the body, in which a line drawn from 

 the centre of gravity of the body falls within the area of both feet placed upon the 

 ground. In the military attitude, the muscles act in two directions (1) to fix the 

 jointed body, as it were, into one unbending column ; and (2) in case of a variation 

 of the equilibrium, to compensate by muscular action for the disturbance of the 

 equilibrium. 



The following individual motor acts occur in standing : 



1. Fixation of the head upon the vertebral column. The occiput may be moved in various 

 directions upon the atlas, as in the acts of nodding. As the long arm of the lever lies in front 

 of the atlas, necessarily when the muscles of the back of the neck relax, as in sleep or death, 

 the chin falls upon the breast. The strong neck muscles, which pull from the vertebral column 

 upon the occiput, fix the head in a firm position on the vertebral column. The chief rotatory 

 movement of the head on a vertical axis occurs round the odontoid process of the axis. The 

 .articular surfaces on the pedicles, and part of the bodies of the 1st and 2nd vertebra?, are con- 

 vex towards each other in the middle, becoming somewhat lower in front and behind, so that 

 the head is highest in the erect posture. Hence, when the head is greatly rotated, compression 

 of the medulla oblongata is prevented (Henke). In standing, these muscles do not require to 

 be fixed by muscular action, as no rotation can take place when the neck muscles are at rest. 



2. Fixed Vertebral Column. The vertebral column itself must be fixed, especially where it 

 is most mobile, i.e., in the cervical and lumbar regions. This is brought about by the strong 

 muscles situate in these regions, e.g., the cervical spinal muscles, Extensor dorsi communis and 

 Quadratus lumborum. 



Mobility of the Vertebrae. The least movable vertebra? are the 3rd to the 6th dorsal ; 

 the sacrum is quite immovable. For a certain length of the column, the mobility depends 

 on (a) the number and height of the interarticular fibro-cartilages. They are most 

 numerous in the neck, thickest in the lumbar region, and relatively also in the lower 

 cervical region. They permit movement to take place in every direction. Collectively the 

 interarticular discs form one-fourth of the height of the whole vertebral column. They are 

 compressed somewhat by the pressure of the body ; hence, the body is longest in the morning 

 and after lying in the horizontal position. The smaller periphery of the bodies of the cervical 

 vertebra? favours the mobility of these vertebra? compared with the larger lower ones, (b) The 



