440 ON THE STRUCTURE OF THE FOOT IN BIRDS. 



PLATE XXIV. 



Fig. 1. Outline of posterior margin (right side) of sternum of Ossifraga gigantea. 

 Reduced. 



2. The same of D apt ion capensis. 



3. The same of Fulmarus glacialis. 



4. The same of Aeipetes antarcticus. 



5. The same of Thalassceca glacialoides. 



6. The same of Prion desolatus. 



7. Sternum and pectoral arch of Cymochorea leucorrhoa, from in front. 



8. The same, from the side. 



9. The same of Fregetta mela/nogastra, from in front. 



10. The same, from the side. 



11. Outline of posterior margin (right side) of sternum of Bulweria columbina. 



12. The same of (Estrelata lessoni. 



13. The same of Adamastor cinereus. 



14. The same of Majaqtteus cpquinoctialis. 



15. The same of Puffinus anglorum. 



16. The same of Pagodroma nivea. 



ibis 188* 66 * ON THE VARIATIONS FROM THE NORMAL 



P.' 386? STRUCTURE OF THE FOOT IN BIRDS.* 



" IN all birds, even in Arcluxopteryx, the fifth digit of the pes remains 

 undeveloped .... Many birds have only three toes, by suppression of 

 the haliux. In the Ostrich, not only the hallux, but the phalanges of 

 the second digit are suppressed .... hence the Ostrich has only two 

 toes." 



" The normal number of the pedal phalanges in birds is (as in ordinary 



Lacertilia) 2, 3, 4, 5, reckoning from the hallux to the fourth digit. 



Among the few birds which constitute exceptions to the rule are the 



Ibis, 1882, Swifts, in which the third and fourth toes have only three phalanges 



p. 387. each (2, 3, 3, 3), and the Goatsuckers and the Sand-Grouse, in which 



the fourth toe only has the number thus reduced (2, 3, 4, 3)." 



Prof. Huxley has described in these words f the nature of the 

 variations from the normal structure of the Avian pes, as regards the 

 number of digits and phalanges composing it, exhibited by various 



* Ibis, 1882, pp. 386-390. 



t ' A Manual of the Anatomr of Vertebrated Animals,' pp. 206, 297. London, 1871. 



