152 ARTICULATION AND SUPPORT 



to the most prominent point of the jaws; and thus the 

 greater share of the weight is in front of the joint. Place 

 the occipital condyles on any point of support, and the 

 head will incline forwards, unless it be held in equilibrio 

 by a force applied behind. The preponderance is greater 

 when the lower jaw is added; and it is still further increas- 

 ed by the accession of the tongue, muscles, and other 

 soft parts. 



This inclination of the head forwards is counteracted in 

 the living body by the extensor muscles ; and their constant 

 exertion is necessary for maintaining the head in equilibrio 

 on the vertebral column. Whenever their contraction is 

 suddenly suspended, as in a person falling asleep in the 

 erect attitude with the head unsupported, that part, aban- 

 doned to the force of gravity, immediately nods forwards. 



The greatest number, and by far the most powerful 

 muscles, are placed at the back of the head, and pass 

 between the posterior surface of the vertebral column and 

 the occiput. The recti postici, obliqui superiores, trachelo- 

 mastoidei, complexi, splenii capitis, and trapezii are balanced 

 by few and inconsiderable muscles in front ; by the recti 

 antici, recti laterales, and longi colli. 



Let a line be drawn according to the plane of the occi- 

 pital foramen ; it will pass from the posterior edge along 

 the surface of the condyles; and, if continued anteriorly, 

 will come out just under the orbits. It forms, in short, 

 almost a horizontal line, which intersects, nearly at right 

 angles, the vertical line of the body and neck, when the 

 head is held straight, without being inclined backwards 

 or forwards. 



In this attitude, the face is in a vertical line, parallel to 

 that of the body and neck ; and consequently the jaws 

 hardly extend in front beyond the forehead. They are very 



the great extensor muscles of the loins and back. The hip-joints are carried 

 forwards, and the feet prolonged in front of the ankle, in order to secure 

 the body against the consequences of this preponderance in the anterior di- 

 rection, the natural effect of which is seen by our falling forwards when 

 muscular action is suddenly suspended ill fainting. 



