LEGS AND FEET OF ICHTHYORNIS. 175 



metatarsus, over the middle element, dies out rapidly downward, and the 

 bone tapers somewhat to near the distal end. Where the diameter 

 is least, the section is nearly oval, but the regularity of the oval is 

 somewhat interrupted by the shaft of the fourth metatarsal, which is indi- 

 cated by a ridge running the entire length of bone. Near its distal end, 

 it is moreover separated from the adjoining third metatarsal by a foramen 

 which is nearly as large as in the Tern, but is separated by a much weaker 

 osseous bar from the interval between the two articular ends of the bones. 

 Of the three distal articular faces, the middle is the largest, and most 

 advanced. The outer or fourth stands but little back of the middle, and 

 is directed well outward, being more oblique than in the Tern. The 

 face of the second metatarsal is considerably behind the other two, and is 

 more oblique than the fourth. It is also the smallest of the three faces. 

 The tlnee articulations are slightly more divergent and oblique than in the 

 Tern, but they are more nearly in a transverse line than in that bird. 

 They are also broader, with less extension vertically. 



The dimensions of the tarso-metatarsal bone in three individuals of 

 Iehthyornis are as follows : 



Measurements of Tarso-metatarsal. {Iehthyornis victor, No. 1739.) 



Length of tarso-metatarsal, 58. mm 



Transverse diameter of shaft, 3.5 



Greatest diameter of distal end, _ 9. 



Transverse diameter of inner articulation, 3.6 



Vertical diameters of inner articulation, 2.6-2.1-3. 



Transverse diameter of median articulation, 2.6 



Vertical diameters of median articulation, 3.8-3.1-4. 



Transverse diameter of outer articulation, 2.6 



Vertical diameters of outer articulation, 3.8-3.-3.4 



Transverse diameter of proximal end, V. 



Measurements of Tarso-metatarsal. {Iehthyornis victor, No. 1464.) 



Greatest diameter of distal end, 9. mm 



Transverse diameter of inner articulation, 3. 



Vertical diameters of inner articulation, 2.9-2.2-3.2 



Transverse diameter of median articulation, 3. 



Vertical diameters of median articulation, 4.-3.5-4. 



Transverse diameter of outer articulation. 2.9 



Vertical diameters of outer articulation, 3.9-2.8-3.2 



