1 8 ANATOMY OF A CHELONIAN. 



22. The Caudal Vertebrae are freely movable, and in 

 the anterior part of the tail proccelous. From the fifth 

 to the tenth, inclusive, they have well-marked rudimen- 

 tary ribs attached to them. None have transverse pro- 

 cesses. Becoming smaller and smaller toward the tip 

 of the tail, they are finally reduced to minute subcy- 

 lindrical masses, without any processes, biit each still 

 possessing a centrum and a neural arch enclosing a 

 neural canal. 



23. The Skull.— After boiling the skull, clean away the 

 soft parts, taking care to leave, in so doing, as much 

 of its cartilaginous parts as possible — the thin plate 

 between the nostrils is especially apt to be removed. 

 When cleaned, make outline drawings of the skull, as 

 seen from behind, from the base, and antero-laterally. 



24. The skull is flattened from above down, and 

 wide from side to side. Note that the brain-case proper 

 is much narrower than the skull', which is expanded 

 posteriorly, to form a pair of ^sx^q post-auditory processes, 

 from which two bony arches proceed forward on each 

 side : one below the orbit to the upper jaw, and the 

 other behind the orbit to the brain-case proper. The 

 temporal fossa is covered in by this arch on each side, 

 and is continuous with the orbital cavity, so that the 

 two form one orbito-temporal fossa. 



25. On the Posterior Aspect of the Skull, note : 



a. The foramen magnum, and below it the single 

 occipital condyle. 



b. On eaqh side of the condyle are two small 

 foramina ; through the more mesial of these, 

 the hypoglossal nerve (i8o, i) passes out. 



