PROFESSOR OWEN ON THE GENUS BINORNIS. 357 



2 lines, near the free end of the bone. The total length of the scapula is 5 inches ; 

 that of the tibia of the same bird is 2 feet 3 inches — a strange disproportion ! The 

 scapulo-coracoid arch exists in this huge wingless bird solely in physiological relation 

 as the lever by which the respiratory muscles act to depress the sternum, expand the 

 thoracic air-cells, doubtless developed as in Apteryx, and so cause the rush of air by 

 the trachea into the lungs. 



DESCRIPTION OF THE PLATES. 



PLATE LIII. 



Fig. I. Upper view of the skull of Dinornis robustus, from the bone-fissure at " Timaru." 

 (The premaxillary is figured about 8 lines too far in advance of the cranium.) 



Fig. 2. Side view of the same skull. (The dentary (32, 32', 32") is figured about half an 

 inch too far in advance of the surangular ( 29') and angular (so), in order to 

 show the articular grooves.) 



Fig. 3. Back view of the cranium of the same skull. 



Fig. 4. Front view of the atlas-vertebra of a large Dinornis. 



Fig. 5. Back view of the same vertebra. 



Fig. 6. Side view of the same vertebra. 



PLATE LIV. 



Fig. 1. Base view of the skull of Dinornis robustus, from the bone-fissure of " Timaru." 

 (The premaxillary is figured about half an inch too far in advance.) 



Fig. 2. Inner or mesial surface of the left tympanic bone of the same skull. 



Fig. 3. The same tympanic bone, viewed from below, e', mastoid condyle ; p, posterior 

 pneumatic foramen ; q, antero-internal pneumatic foramen ; k, orbital pro- 

 cess ; pt, articular surface for pterygoid ; h i, postero-external condyle, 

 i', antero-internal condyle, for the articular part of the mandible. 



Fig. 4. Upper view of mandible of the same skull. 



PLATE LV. 



Fig. 1 . Side view of the skull of Dinornis robustus, from the skeleton in the arenaceous 



deposit at " Manuherikia." 

 Fig. 2. Outside view of scapulo-coracoid bone of the same skeleton. 

 Fig. 3. Inside view of the same scapulo-coracoid bone. 

 Fig. 4, Posterior margin of the same bone, showing the ridge (r) in place of a glenoid 



cavity. 



