ANATOMY. 



shifting upon one another, so as to break 

 the line of the canal as often as the body 

 moves or twists, or the joints gaping ex- 

 ternally, whenever the body is bent for- 

 wards, and the spine thereupon made to 

 take the form of a bow. These dangers, 

 which are mechanical, are mechanical- 

 ly provided against. The vertebrae, by 

 means of their processes and projections, 

 and of the articulations which some of 

 these form with one another at their ex- 

 tremities, are so locked in and confined, 

 as to maintain, in what are called the bo- 

 dies or broad surfaces of the bones, the 

 relative position nearly unaltered ; and to 

 throw the change and the pressure pro- 

 duced by flexion almost entirely upon the 

 intervening cartilages, the springiness 

 and yielding nature of whose substance 

 admits of all the motion which is necessa- 

 ry to be performed upon them, without 

 any chasm being produced by a separa- 

 tion of the parts. I say of all the motion 

 which is necessary; for, although we 

 bend our backs to every degree almost of 

 inclination, the motion of each vertebrae 

 is very small : such is the advantage 

 which we receive from the chain being 

 composed of son;any links. Had it been 

 composed of three or four bones only, in 

 bending the body the spinal marrow must 

 have been bruised at every angle. 



The substances which connect the bo- 

 dies of the vertebrae to each other, called 

 the intervertebral cartilages, are thick, 

 firm, and elastic. They are similar in 

 shape, and nearly so in size, to the bones 

 which they join. They are thicker before 

 than behind, so that, when we stoop for- 

 wards, the compressible cartilage, yield- 

 ing to the force, brings the surfaces of the 

 adjoining vertebrae nearer to a state of 

 parallelism than they were before, instead 

 of increasing the inclination of their 

 planes, which must have occasioned a 

 fissure or opening between them : and 

 their elasticity restores the body to its 

 former state, when the compressing force 

 ceases. 



In order still further to increase the 

 strength of the compages, and to add a 

 greater security against luxation, the ver- 

 tebrae are articulated to each other by 

 means of the processes before mentioned. 

 And these processes so lock in with and 

 overwrap one another, as to secure the 

 body of the vertebra, not only from acci- 

 dentally slipping, but even from being 

 pushed out of its place by any violence 

 short of that which would break the bone. 

 The roots of the spinous processes are 

 also joined to each other by very strong 



and highly elastic ligamentous substances 

 which will tend powerfully to restore the 

 column after it has been bent forwards. 



The general result is, that not only the 

 motions of the human body, necessary for 

 the ordinary offices of life, are performed 

 with safety, but that it is an accident 

 hardly ever heard of, that even the ges- 

 ticulations of a harlequin distort his 

 spine. 



The ribs are articulated by their pos- 

 terior extremities to the bodies and to 

 the transverse processes of the vertebrae, 

 and the true ribs are also joined by means 

 of their cartilages to the sternum. Two 

 great advantages are derived from the 

 ribs having this cartilaginous portion 

 The effect of blows, or of any accidental 

 violence, is eluded, by the flexibility 

 which they thus obtain ; and the elastic 

 power of the cartilages restores the ribs 

 to their former position, after they have 

 been raised by the intercostal muscles in 

 breathing. 



Joints of the upper extremity. The clavi- 

 cle is articulated to the sternum at one 

 end, and to the scapula at the other. 



The shoulder is formed by a round 

 head of the humerus, which plays in a 

 cup of the scapula ; and the ends of the 

 bones are enclosed by a thick and strong 

 ligamentous membrane, called the orbi- 

 cular ligament. There is here, therefore, 

 every latitude of motion allowed. 



In the elbow, on the contrary, the joint 

 is a mere hinge : lateral motion is restrain- 

 ed by strong ligaments placed at the sides 

 of the joint, and the fore -arm can there- 

 fore be moved only forwards and back- 

 wards. This joint is formed between the 

 ulna and the humerus. 



The wrist is formed by the junction of 

 the radius with the first phalanx of carpal 

 bones. Its motion is very little more than 

 that of a ginglymus. The rotation of the 

 hand and wrist, or what anatomists call 

 the pronation and supination, are per- 

 formed by the radius revolving round the 

 ulna, and carrying the hand with it. In 

 this case the elbow joint is fixed ; neither 

 does the joint of the wrist move ; but the 

 radius moves freely round the ulna, and 

 the hand is included in the motion. The 

 pronation and supination of the hand are 

 well exemplified in the use of the broad- 

 sword, and in cudgel-playing. 



The carpal and metacarpal bones are 

 united by joints and ligaments, but have 

 no obvious motion on each other. The 

 phalanges of the fingers are also articu- 

 lated by ginglymi. 



The bones of the pelvis are inseparably 



