160 Practical Zoology. 



squarely, edge to edge, or does one pair naturally rest back of 

 the others ? If so, which are in front in the resting position ? 

 Can the lower jaw be moved forward and back ? Do the lower 

 incisors always come up in the same position in relation to the 

 upper incisors ? Note the angle at which the incisors are set. 

 Now examine the grinding teeth, or molars. How many are 

 there in each half-jaw? What is their shape? Are there 

 ridges on their grinding surfaces ? If so, in what direction do 

 they run ? How is this related to the chief chewing motion ? 

 Are all the molars set at the same angle ? Why any difference ? 

 At this point, if possible, look again at a live rabbit and watch 

 the process of eating. How are the jaws moved, and how do 

 the motions stand related to all these facts about the teeth ? 



4. Take a well-cleaned lower jaw of a rabbit. Embed it in 

 sealing wax on a small block of wood, with the inner face of the 

 jaw uppermost. With a grindstone, grind away half of the 

 incisor and the surrounding jawbone. Is there a distinct root ? 

 Is the tooth equally hard throughout? The front part is enamel. 

 The bulk of the tooth consists of dentine, or ivory. Grind away 

 half of the molars and the bone in which they are set. Do any 

 of these teeth continue growing after the rabbit has reached 

 maturity ? Is it a serious matter for a rabbit to lose one of its 

 front teeth ? Why ? 



5. Each separate piece of the backbone is a vertebra. The 

 vertebrae of the neck are called cervical vertebrae. The vertebrae 

 that bear ribs are thoracic. Following the thoracic vertebrae are 

 the lumbar vertebrae. After these, are several grown together 

 and supporting the bones of the pelvis ; they constitute the 

 sacrum. Last, the vertebrae of the tail, the caudal vertebrae. How 

 many are there of each of these kinds? How many in all? 

 Review the whole spinal column, comparing the different parts. 



Take a vertebra from the middle of the thorax and examine it 

 carefully. Its main part is the body or centrum. On the dorsal 

 side is an arch, the neural arch, through which the spinal cord 

 passed. Above the arch is a projection, the neural spine, the 



