116 OSTEOLOGY OF INIA GEOFFEENSIS AND PONTOPOEIA BLAINVILLIl. 



DESCRIPTION OF THE PLATES. 



The figures in Plates XXV., XXVI., and XXVII. are drawn from the skeleton of the 

 young Inia geoffrensis described above. 



PLATE XXV. 



Fig. 1. Upper surface of the cranium and vertebral column of Inia geoffrensis. One- 

 fourth the natural size. 

 Fig. 2. Side view of the skull and vertebral column. One-fourth the natural size. 

 Fig. 3. Bones of the right pectoral limb. Half the natural size. 



PLATE XXVI. 

 Fig. 1. Inferior surface of the cranium of Inia geoffrensis. Half the natural size. 

 Fig. 2. Superior sui-face of the mandible. Half the natural size. 

 Fig. 3. A maxiUary tooth from the left side, the fourth from the posterior end of the 



series. Natural size. 

 Fig. 4. The basi- and thyro-hyals. Half the natural size. 

 Fig. 5. One of the stylo-hyals. Half the natural size. 



PLATE XXVII. 



Details of the osteology of Inia geoffrensis. All the figures half the natural size. 



Fig. 1. Anterior surfaces of the seven cervical vertebrse. 

 Fig. 2. The thirteen ribs of the right side. 

 Fig. 3. Side view of the sternum. 



a. Anterior process. 



b. Lateral process. 



c. Surface for attachment of cartilage of first rib. 



d. Sui'face for attachment of cartilage of second rib. 

 Fig. 4. Internal surface of sternum. 



Fig. 5. External surface of sternum. 



PLATE XXVIII. 



Skull of adult Pontoporia blainvillii. All the figures (except fig. 5) half the 

 natural size. 



Fig. 1. Side view of cranium. 

 Fig. 2. Side view of mandible. 

 Fig. 3. Upper surface of cranium. 

 Fig. 4. Inferior surface of mandible. 



Fig. 5. A maxillary tooth from the left side, the fourth from the posterior end of the 

 series. Twice the natural size. 



