THE SKULL. 35 



f 



jects a process which surmounts the body of the axis, namely, 

 the odontoid process, and round this the atlas, carrying with 

 it the skull, revolves as on a pivot. The motion, however, 

 is limited by two lateral bands, the check ligaments, which 

 pass out from the top of the odontoid process to be attached 

 to the sides of the foramen magnum, the opening in the 

 skull by which the cranial cavity is made continuous with 

 that of the spinal column. By the study of development and 

 the anatomy of different animals, it is well ascertained that 

 the odontoid process is really the body of the atlas, which 

 has become fastened to the top of the body of the axis, and 

 remained separated by a joint from the other parts of the 

 bone to which it in one sense belongs. 



18. The skull consists of cranium and face. The cranium, 

 or part enclosing the brain, is counted as having eight bones. 

 But it is right that even a tyro should understand that 

 various of these bones consist of different elements which 

 have become fused together at an early age, while some of 

 what are considered as distinct bones are also fused together 

 in every adult. The word " bone" is, therefore, used some- 

 what arbitrarily in speaking of the bones of the skull. The 

 occipital bone forms part both of the base and the roof, and 

 is pierced by the foramen magnum. The other bones of the 

 roof are the two parietals and the frontal, which in the child 

 is divided down the middle like the parietals. The frontal 

 not only forms a large part of the vault of the skull, but also 

 the roofs of the orbits or sockets of the eyeballs. In. the 

 base of the skull, a complex bone, the sphenoid, formed by 

 the junction of many elements, and primarily divisible into 

 an anterior and posterior part which are distinct in most 

 animals, extends forwards from the occipital, with w^hich it 

 is thoroughly united in the adult, and reaches the orbital 

 plates of the frontal ; while the interval between the orbits 

 is filled in by the upper part of a delicate and .likewise com- 

 plex bone, the ethmoid, which is pierced with foramina for 

 the filaments of the nerves of smell, and takes much greater 

 part in the formation of the cavity of the nose than in com- 

 pleting the cranial walls. 



Lastly, on the sides of the skull, and projecting into its 

 base between the sphenoid and occipital, are the temporal 



