PATELLA OF HESPERORNIS. 93 



The Patella. (Plates XV and XX.) 

 The patella in Hesperornis regalis is a large bone, and entirely distinct 

 from the tibia. In its general proportions, it resembles the patella in 

 Podiceps. It differs materially, however, in being perforated by a large 

 foramen for the tendon of the ambiens muscle, agreeing in this respect 

 with the patella of the Gannet (Sula bassana, Briss.). The patella is much 

 compressed transversely. Seen from the side, it is triangular in outline, 

 and the outer surface is concave. When in position, its longer axis was 

 nearly parallel with the axis of the tibia. Its lower extremity bears a large 

 twisted articular face for union with the femur, and the lower posterior half 

 of the inner side is roughened for attachment to the cnemial spine. 



The position of the patella in the skeleton is shown in Plate XX. 

 TThen at rest, it extended in front of the anterior margin of the ilium, and, 

 by its muscular attachments, added greatly to the power of the posterior 

 limbs in swimming. The superior extremity is obtusely pointed, and the 

 outer margin is arcuate. 



The following measurements are taken from the patella of three 

 specimens of Hesperornis regalis, and one, number 1474, of Hesperornis 

 crassipes : 



Measurements of Patella. (No. 1207.) 



Total length of patella, 98.0 mm 



Length of posterior side, 87.0 



Greatest diameter of articulation, 37.0 



Least diameter of articulation 25.0 



Distance from foramen to upper end of patella, 71.0 



Vertical diameter of foramen, 6.0 



(No. 1476.) 



Total length of patella, 100.0° 



Length of posterior side, 84.0 



Greatest diameter of articulation (approximate), 35.0 



Least diameter of articulation (approximate), 25.0 



Distance from foramen to upper end of patella, 75.0 



