OSSEOUS SEMICIRCULAR CANALS OF BIRDS. 26 1 



ing families : Struthionidae, Spheniscidae, Ciconiidae, Tinamidae, 

 Phasianidae, Aphrizidae, Laridae, Strigidae, Stercorariidae, Alcedi- 

 nidas, Bubonidae, and Hirundinidae. 



The exterior canal is larger than the posterior canal in the 

 families : Phalacrocoracidae, Cuculidae, Tyrannidas, Corvidas, Icte- 

 ridae, Fringillidae, Mniotiltidae, Troglodytidae, and Turdidae. 



The posterior and exterior canals are equal in the families : 

 Pelecanidae, Tanagridae, and Paridae. 



The posterior canal is larger than the exterior, or the posterior 

 and exterior canals are equal, in the family Falconidas. 



The exterior canal is larger than the posterior canal, or the 

 exterior and posterior canals are equal, in the families; Ardeidae, 

 Cathartidae, Tetraonidae, Caprimulgidae, and Picidae. 



Falling under none of the above groups are the families : Ana- 

 tidae, Charadriidae, Scolapacidae, and Columbidae ; in each of 

 which there are great generic differences of the relative sizes of 

 the canals. 



3. TYPES OF CANALS. 



In taking the measurements of the canals, I noticed that the 

 position of the canals with reference to one another or the angle 

 at which they are joined, was not always the same. There are 



FIG. i. FIG. 2. FIG. 3. FIG. 4. FIG. 5. 



five types, though these intergrade, under which all species may 

 be grouped (Figs. 1-5). It will be noticed that these are differ- 

 ences mainly of the anterior canal, depending on its length. 



Type I. (Fig. i), the genera Struthio and Tmamns. 



Type II. (Fig. 2), Cathartidae, Geococcyx, Scolopacidae, Laridae, 

 Stcrcorarins, Colnmba, Zcnaidnra, Ceryle, Caprimulgidae, Stri.v, 

 Asia, Tetraonidae. 



Intermediate between types III. and V. are the genera Turtur, 

 Melanerpes, and Dryobates. 



