212 THE BIOLOGY OF THE ANIMAL 



an olfactory capsule. Examine the lower jaw, 

 the mandible or inferior maxilla. What is 

 its shape ? What is its position when the mouth 

 is closed ? Does it bear teeth ? Are its two sides 

 immovably connected ? Of how many parts is 

 each half of the mandible composed? On its 

 upper edge find a groove in which lies Meckel's 

 cartilage. Where does this cartilage begin? 

 How far does it extend ? Do j'ou find any fo- 

 ramina in the lower jaw ? If so, where are they ? 

 Draw the mandible as seen from above. Notice 

 that the upper part of the skull consists of a sys- 

 tem of parts attached to the cranium and the 

 sense capsules. Examine the posterior end of 

 the skull and find a large opening, the foramen 

 magnum. What is its shape ? Size ? What is 

 its relation to the neural canal in the spinal col- 

 umn ? To the cranial cavity ? Find a convex 

 tubercle, the occipital condyle, on each side of 

 the foramen magnum. What is the shape of 

 the condyle ? What is the direction of its 

 longer axis? The nature of its surface? Its 

 relation to the atlas ? Each condyle is borne 

 upon one of the exoccipital bones. What is 

 the relation of these bones to the foramen mag- 

 num ? What is their shape ? Do the exoccipital 

 bones form any part of the auditory capsules? 

 Note that each condyle is pierced by a foramen 

 which is the exit of the tenth cranial nerve 

 (vagus). Notice on each side the ridge along 

 "which is the junction between the exoccipital 

 bone and the pro-otic bone. What is the shape 

 of the latter? What part of the auditory capsule 

 does it form ? Is any part of the front of the 



