XIII 



PHYLUM CHORDATA 



363 



approaching Birds in certain features of their structure, others coming nearer 

 the earliest fossil Crocodiles. The surface was in some covered with a bony 



FlG. 1027. Iguanodon bernissartensis. One sixtieth natural size. co. coracoid ; is. 



ischium ; p. pubis (pectineal process) ; pp. post-pubic process (pubis) ; sc. scapula 

 / V, I IV, digits. (From Zittel, after Dollo.) 



armour, sometimes armed with long spines. The fore- and hind-limbs were 

 in some equally developed ; in others the hind-limbs were much more 

 powerful than the fore-limbs, and in many their structure appears adapted 

 to a bipedal mode of 

 progression (Fig. 1027). 

 The centra are in 

 general amphiccelous, 

 but vary greatly. The 

 sacral region usually 

 comprises 3 to 6 verte- 

 brae. The thoracic ribs 

 have double heads. Ab- 

 dominal ribs are some- 

 times present. The 

 sternum was incom- 

 pletely ossified, and an 

 episternum is absent. 

 There is no parietal 

 foramen. There are 

 complete upper and 

 lower temporal arches, 

 and the fossa is divided 

 into upper and lower 

 parts by a bar formed from the post-frontal and squamosal. Ectopterygoids 

 are present. The quadrate is firmly fixed. In the pectoral arch the scapula 

 is very large, the coracoid small, and the pro-coracoid and clavicle absent. 



1028. Teeth of Iguanodon mantelli. A, from the 

 inner, B, from the outer side. (From Zittel, after Mantell.) 



