CRANIUM. 37 



The cranium is a box with a thick floor (Fig. 1), con- 

 tinuing forwards the partition which in the trunk separates 

 the neural from the haemal cavity. On its under side 

 (Fig. 20) are many small apertures through which nerves 

 and blood-vessels pass in or out, and one larger one, the 

 foramen magnum, through which the spinal cord passes 

 in to join the brain. 



The cranial bones (Fig. 16) are the following : 1. The 

 occipital bone, 0, unpaired, and having in it the fora- 

 men magnum. It lies at the back of the skull. 2. The 

 frontal bone, F, also unpaired, lies in the forehead. 3. 

 The parietal bones, Pr, two in number, meet one another 

 above the middle of the crown of the head, and form a 

 great part of the roof and sides of the skull. 4. The tem- 

 poral bones, T, one on each side, opposite the temples ; 011 

 the exterior of each temporal bone is a large aperture 

 leading into the ear cavity, which is contained in this 

 bone. 5. The sphenoid bone, unpaired, and lying in the 

 middle of the base of the skull, but sending out a wing,-^ 

 which reaches some way up each side, just in front of the 

 temporal. G. TJie ethmoid bone, E, forms the partition be- 

 tween the brain and nose chambers, and part of that be- 

 tween the nose and the eye socket. 



The facial skeleton. The majority of the face bones 

 are in pairs, but two are single ; one of these is the lower 

 jaw bone or mandible, Md, Fig. 16 ; the other is the vomer, 



With what is the floor of the cranium continuous? Where does 

 the cranium present holes through it? What are most of these aper- 

 tures for? What is the largest aperture called? What enters the 

 brain case through it? 



Name the cranial bones. State where each lies. Through which 

 does the foramen magnum pass? Which contains the ear chamber? 

 Which of them are unpaired? 



