128 SKELETON. 



hole is oval, the long diameter extending from before back- 

 wards. Its anterior inferior margin, on either side, is furnished 

 with a condyle,- for articulating with the first vertebra of 

 the neck. These condyles are long eminences tipped with 

 cartilage, which converge forwards, so that lines drawn 

 through their length would meet an inch in front of the fora- 

 men magnum; they recede behind: their internal margins are 

 deeper than their external. The condition of their articular 

 surfaces is therefore such, that they permit flexion and exten- 

 sion of the head, but not rotation. The anterior edge of the 

 foramen is thicker than the posterior. This foramen transmits 

 the medulla oblongata, the vertebral arteries and veins, and 

 the spinal accessory nerves. 



The external surface of the occiput presents, half way be- 

 tween the foramen magnum and the upper angle of the bone, 

 the occipital protuberance, from the lower part of which a 

 small vertical ridge is extended in the middle line to that 

 foramen. Into the ridge is inserted the Ligamentum Nuchae. 

 From either side of the protuberance an arched ridge is ex- 

 tended to the lateral angle of the bone ; it is the superior semi- 

 circular ridge or line, from which arise the occipito frontalis 

 and the trapezius muscles, and into it is inserted a part of the 

 sterno cleido-mastoideus. Below this about an inch is the in- 

 ferior semicircular ridge, more protuberant, but not so dis- 

 tinctly marked in its whole course. Into the inner space, 

 between the upper and lower ridges, is inserted the complexus 

 muscle, and into the outer space between the same, the sple- 

 nms muscle. The lower ridge is principally occupied by the 

 origin of the superior oblique muscle of the neck. 



The inner space between this ridge and the great foramen, 

 gives origin to the rectus posticus minor, and the outer space to 

 the rectus posticus major. Into a small elevation, leading from 

 the outside of the condyle directly to the margin of the bone, 

 is inserted the rectus capitis lateralis. 



In a depression behind each condyle is the posterior condy- 

 loid foramen, which conducts a cervical vein to the lateral sinus. 

 Passing through the base of the condyle, and having its orifice 

 in front, is the anterior condyloid foramen for conducting the 

 hypoglossal nerve to the toncm*. 



