43 8 CROCODILIA 



kinds, especially in the Alligators, most of the upper teeth overlap 

 laterally those of the lower jaw. In most species of Crocodilus 

 the overlapping is less marked and the teeth partly interlock, but 

 the fourth mandibular tooth, generally the strongest and longest, 

 is received into a lateral notch at the junction of the pre- 

 maxillary and maxillary. Frequently those of the longer lower 

 teeth which fit into pits of the upper jaw, gradually transform the 

 pits into holes by continued pressure upon the bone, and in old 

 specimens the tip of the lower tooth may even perforate and 

 stand out above the skin of the snout. 



The vertebrae are solid, but remnants of the notochord per- 

 sist for a long time in the middle of the centra. These are still 

 amphicoelous in the Jurassic Eusuchia, and there were probably 

 considerable intervertebral portions of the notochord. From the 

 Lower Chalk onwards the vertebrae are procoelous, with the 

 exception of the first caudal vertebra, which has a knob at 

 either end, so that naturally the posterior of the two sacral verte- 

 brae is opisthocoelous. This peculiar formation of the first 

 caudal is probably correlated with the flexibility of the tail. 



. Cartilaginous intercentral rings, pads or menisci, occur 

 regularly throughout the vertebral column, unless they are 

 abolished by fusion of adjoining vertebrae. It is most instructive 

 to follow the attachment of the ribs in one and the same 

 individual. The position of the capitulum, vertically below the 

 tuberculum in the neck, changes in the thorax into one in which 

 the capitulum lies anterior to the tuberculum and in the same 

 horizontal plane with it. Moreover, whilst on the cervical 

 vertebrae the capitulum is carried by the centrum (enclosing 

 with the tuberculum a typical transverse canal for the vertebral 

 artery, etc.), further back it moves its point of attachment up- 

 wards, lying right upon the neuro-central suture on the tenth and 

 eleventh vertebrae. From the twelfth vertebra backwards both 

 capitulum and tuberculum are carried by the transverse process 

 or diapophysis of the neural arch. The ribs of the five or six 

 lumbar vertebrae are merely vestigial or absent. The ribs of the 

 two sacral vertebrae are very stout, fusing in the adult with both 

 centrum and neural arch. Some of the anterior caudal vertebrae 

 also carry ribs, attached across the neuro-central suture ; long 

 before maturity they fuse with their vertebrae, and then look like 

 transverse processes. Most of the caudal vertebrae carry also a 



