SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 



131 



tarsus ; — a very rare condition in existing birds, and even absent in P. flavirostris, 

 where only the usual outer foramen seems to be present. 



At the back of the shaft there is a low median ridge running down from the 

 lowermost point of the hypotarsus to bifurcate below. One limb is lost on the pos- 

 terior surface of the mid-trochlear process, the other on the outer one, while between 

 them occurs the outer of the two perforating foramina just described above. Upon 

 either side of this ridge, the shaft upon this aspect is also grooved in the longi- 

 tudinal direction, but not so deeply as it is in front. Placed side by side in the 

 anterior groove of the bone, just below the head, we find a pair of perforating foram- 

 ina. They make their exit one upon either side of the lower part of the hypo- 

 tarsus behind ; each one lying in a postero-longitudinal groove, to which mention 

 has just been made in the last paragraph. The sides of the shaft of this bone of the 

 leg are more or less flattened, and the tubercle for the insertion of the tibialis anticus, 

 is very small. The first metatarsal is free, being long and flake-like, and articulates 

 by its entire outer margin, with the postero-internal edge of the shaft of the tarso- 

 metatarsus. Pes has what is usually termed the normal arrangement and number 

 of joints to the several toes, i. e., 2, 3, 4 and 5 joints, to the hallux, second, third and 

 fourth digits respectively. Exceedingly slender and long, the basal joint of hallux 

 is tipped off with a small, slightly curved ungual phalanx. The terminal pha- 

 langes of the three anterior toes are relatively much stouter, thicker, but exhibit 

 about the same proportionate amount of curvature. With respect to the shafts of 

 the intermediate joints, it is to be noted that they are long, slender, and exhibit but 

 very little curving; while the articular ends of these bones are but very slightly 

 enlarged. Indeed, the skeleton of the foot in the Phaethonidss is in reality deli- 

 cately constructed. 



Table. 



Toes and their joints. 



P. fl'ivirostris. 

 Measurements in mm. 



Remarks. 





\ Basal joint 



11 



> 



From this it will be seen that 



Hallux or First Toe. ■ 



Ungual " 



4 J 

 15 

 12 



5 

 12 

 11 

 10 



5.1 

 10 1 



8 



L 



4 J 



the length of the skeleton of 

 the middle toe is about f the 





f Basal " 



Second or Inner Toe. ■< 



Second " 



length of the tibio-tarsus. On 





Ungual " 



the other hand it is longer than 





f Basal " 



either the femur or the tarso- 





Second " 



metatarsus. 



Third or Middle Toe. <| 



Third " 







Ungual " 



f Basal " 







Second " 





Fourth or Outer Toe. ■{ 



Third " 













rourth 







[Ungual " 





