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- Diagram of the typical vertebra. 
. Back view of a lower cervical vertebra of a Bird (Pelecanus onocrotalus), showing 
. A vertical longitudinal section of an anterior dorsal vertebra of the Streplospondylus 
- A vertical longitudinal section of a middle dorsal vertebra of the Cetiosaurus medius, 
. A vertical longitudinal section of the dorsal vertebra of the Zeleosaurus Chapmanni, 
PLATE 4. 
CROCODILIA.— Vertebral Elements and Systems. 
the four canals about the centrum : the upper or neural canal formed by the 
neurapophyses; the side canals for the vertebral arteries and sympathetic 
nerves formed by the parapophysis, diapophysis, and pleurapophysis; the 
lower canal formed by the perforation of the hypapophysis, analogous to the 
hæmal arch in the tail. 
À vertical longitudinal section of the dorsal vertebra of a Crocodile (Crocodilus 
biporcatus), showing the anterior concavity and posterior convexity of the 
centrum, forming the characters of the > proccelian’ type of vertebra. 
Cuvieri, showing the anterior convexity and posterior concavity of the centrum, 
forming the characters of the ‘ opisthoccelian’ type of vertebra. 
showing the anterior flatness and posterior concavity of the centrum, forming 
the characters of the ‘ platyccelian’ type of vertebra. 
showing the concavity of both ends of the centrum, forming the character of 
the ‘amphiccelian’ type of vertebra. 
A similar section of the centrum of the dorsal vertebra of a young Ichthyosaurus 
communis, showing the extreme degree of the amphicoelian character in that 
genus. 
