102 



HIGH SCHOOL ZOOLOGY. 



Fig. 74— Tortoise-shell Turtle. Erctmochclys imbricata. ^j. 



plates beneath. The latter belong to the exoskeleton and are 

 arranged in tlie form of a box, which shelters the greater part 

 of the ti'unk, and which is divisible into two parts, the dorsal 

 carapace, and the ventral plastron, connected laterally with 

 each other for but a short distance in this species. In the former 

 we recognise a median row, of which the foremost, the nuchal 

 plate, is the lai'gest and is unconnected by bone with the verte- 

 bral column, while the eight neural plates which succeed it are 

 co-ossified with the spines of the underlying eight (second to 

 ninth) dorsal vei-tebrte, and the three pygal plates which term- 

 inate the median row, are again free from the vertebrje beneath. 

 Extending laterally from the neural plates are the eight pairs of 

 costals, which overlie the second to ninth ribs, and extend out 

 ward for the greater part of the length of these ; however, the 

 free tips of the ribs alone are seen to join the bony marginal 

 plates. From this point they are not continued towards the 

 ventral middle line ; the bones of the plastron have, therefore, 

 no relation to them. 



