CRANIAL BONES. 



Human Body, however, these bones very soon ankylose 

 with others or with one another; although they remain 

 distinct throughout life in the skulls of very many lower 

 animals. On the base of the skull, besides many small 

 apertures by which nerves and blood-vessels pass in or out, 

 is a large aperture, the foramen magnum, through which 

 the spinal cord passes in to join the brain. 



The cranial bones are the following: 



1. The occipital bone (Fig. 26, 

 0) unpaired and having in it the 

 foramen magnum. It is made 

 up by the fusion of the basi-oc- 

 cipital with other flatter bones. 

 2. The frontal bone (Fig. 26, F), 

 also unpaired in the adult, but 

 in the child each half is a sep- 

 arate bone. 3. A pair of thin plate- 

 like parietal bones (Fig. 26, Pr) 

 which meet one another along the 

 middle line in the top of the 

 skull, and roof in a great part of 

 the cranial cavity. 4. A pair of 

 temporal bones (Fig. 26, T), one 

 on each side of the skull beneath 

 the parietal. On each temporal 



bone is a large aperture leading Above this are the paired open- 



. i ings of the posterior nares, and 



into the ear Cavity, the essential a short way above the middle ol 



, ! t -i , . the figure is the large median 



parts Of the Organs OI hearing f orart ?en magnum, with the bony 





being contained in these bones. 

 5. The sphenoid bone, made up atlas, on its sides, 

 by the union of the basi-sphe- 



noid &i\&pre- sphenoid (lying on the base of skull in front 

 of the basi-occipital) with one another and with flatter 

 bones, is seen partly (Fig. 26, S) on the sides of the cranium 

 in front of the temporals. 6. The ethmoid, like the sphe- 

 noid, single in the adult, is really made up by the union of 

 a single median basi-ethmoid with a pair of lateral bones. 

 It closes the skull cavity in front, and lies between it and 

 the top of the nasal chambers, being perforated by many 



