STRUCTURE OF THE FOOT IN BIRDS. 147 



part of wbich there usually rises an intercondyloid tuber- 

 osity. The entocondyloid cavity is usually the largest 

 and deepest : it is so in the raven, in which the base of the 

 intercondyloid tubercle extends over the whole of the in- 

 tercondyloid space. There are three calcaneal processes : 

 one, called the "entocalcaneal," projects from below the 

 entocondyloid cavity, and from the back part of the upper 

 end of the entometatarse ; a second, called the " mesocal- 

 caneal," from the intercondyloid tract and the mesometa- 

 tarse, and the third called " ectocalcaneal," from behind 

 the ectocondyloid cavity and the ectometatarse. These 

 three processes are united together by two transverse 

 plates circumscribing four canals, two smaller canals being 

 further carried between the ento and meso-calcaneal pro- 

 cesses. The primitive interosseous spaces are indicated 

 by two small foramina at the upper and back part of the 

 shaft, which converge as they pass forward, and terminate 

 by a single foramen at the fourth part of the anterior con- 

 cavity. A similar minute canal is retained between the 

 outer and middle metatarsals, near their distal ends ; each 

 metatarsal then becomes distinct, and develops a convex 

 condyle for the proximal phalanx. The middle one is 

 the largest, and extends a little lower than the other two: 

 it is also impressed by a median groove ; the more com- 

 pressed lateral condyles are simply convex, and are of 

 equal length. A rough surface, a little way above the 

 inner condyle, indicates the place of attachment of the 

 small metatarsal of the hallux. 



In the swan and other anserine birds the calcaneal 

 prominence presents four longitudii^l ridges, divided by 

 three open grooves, the innermost ridge being the largest; 

 the shaft is subquadrate, with the angles rounded, and 

 none of the surfaces are channelled. The inner condyle 



