SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 149 



the proximal one. An oblique bridge, to confine the extensor tendons, is extended 

 across the deep groove that contains them during Hfe. Nearly parallel with each 

 other, the condyles are wide apart, prominent and convex in front, to become sup- 

 pressed and low and thin -crested behind. 



The fibula has the usual form seen in birds, but is here particularly interesting 

 from the fact that it does not anchylose with the shaft of the leg-bone until it arrives 

 at the middle of its lower third, and even from this low point the remainder of the 

 bone, including an oval "external malleolus," stands out quite prominently. This 

 rare condition of things has been pointed out also by me as occurring in Uri- 

 nator lumme. 



Siila bassana has a long oval patella, obliquely marked across its anterior surface 

 by a groove for the tendon of the ambiens muscle. 



The tarso-metatarsus in Sula is strikingly large in its proportions when compared 

 with the other bones of the limb. In length it is a little more than half as long 

 as the tibiotarsus, but being wider and broader it appears much more massive. Its 

 hypo-tarsus presents three short, longitudinal elevations of unequal sizes. These 

 inclose two tubular passages for tendons, and are grooved themselves besides. In 

 other specimens they are flat, and the two outer elevations may posteriorly meet, 

 thus creating a vertical perforation rather than a groove. The back of the shaft is 

 flat, but in front it is much scooped out above, where it shows two antero-posterior 

 perforations. 



At the distal extremity three large trochlear projections present themselves. 

 They are separated from one another by wide clefts of about an equal depth. These 

 trochlese are placed nearly side by side, the middle one being the lowest down, the 

 inner next, and the outer one the most elevated. Their median grooves are best 

 marked behind, but in addition the internal trochlea presents a deep, vertical notch 

 upon its outer aspect. 



The usual arterial perforation pierces the bone above the cleft found between the 

 outer and middle projections, a groove leading into it from above. 



The accessory metatarsal is rather an elongated bone, swung in the usual way 

 by ligaments to the lower part of the shaft. 



The basal joint of the hallux, which it supports, is comparatively more slender 

 for its length than the other joints of the foot. 



For the three anterior toes these latter are, in number and arrangement, the same 

 as in the vast majority of the class. They present all the characters usuall}' 

 attributed to the phalanges of the podal digits in birds, and are well proportioned, 

 both as regards their relative calibers and lengths. 



