148 ANATOMY OF THE WOOD RAT 



intimately concerned with the epicondyloid ridge, while the 

 origins of the extensores digiti quinti and carpi ulnaris belong 

 more strictly to the lateral epicondyle proper. The latter is 

 to all intents merely a continuation of the lateral articular 

 eminence, although they have different centers of ossifica- 

 tion. The chief eminence of the lateral portion of the sur- 

 face of articulation is the capitellum, cranially situated, 

 which articulates with the radius. 



The more distal portion is a part of the trochlea, articu- 

 lating with the ulna. Proximad of the capitellum is the ect- 

 epicondyloid foramen, always present save in the left humerus 

 of a single specimen of Teonoma, in which the foramen is 

 barely closed by a thin bony membrane. In others it varies 

 somewhat in size. 



The lateral epicondyle is situated a trifle nearer the hu- 

 meral axis than is the medial, and much nearer the anti- 

 brachial axial center. The medial is considerably the more 

 slender, and upon it originate eight muscles — the first and 

 second heads of the flexor digitorum profundus, palmaris 

 longus, flexores digitorum sublimis and carpi radiahs, prona- 

 tor teres, and anconeus. There is no appreciable variation 

 of a subgeneric nature in the shape of this item, however, 

 but there is some shght individual difference in its precise 

 conformation. 



Directly proximad of the trochlea is usually situated the 

 entepicondyloid foramen, which is quite variable. In six 

 Homodontomys it is present and in four absent, the skeletons 

 being bilaterally symmetrical in this respect; in three 

 Neotoma it is present; and in five Teonoma of the form 

 cinerea it is present and in one of the form occidentalis it is 

 absent. When absent it is not merely a case of a thin septum 

 being present, but all signs of it are obhterated and the de- 

 pressions upon either aspect of the bone are filled with bony 

 tissue. 



