The =humerus= is relatively very long, rather slender, and has a slight spiral twist. The shaft is somewhat compressed laterally, especially in its upper two-thirds; this part is curved in varying degree, convex in front. The deltoid tuberosity has the form of a low ridge, and it is continued by a crest which runs upward and backward and bears a tubercle on its upper part. Another line runs from it down the anterior aspect and forms the inner boundary of the very shallow musculo-spiral groove. The nutrient foramen is about in the middle of the posterior surface. A slight elevation on the proximal third of the inner surface represents the teres tubercle. The head is long and strongly curved from before backward. The neck is better marked than in the horse. The undivided external tuberosity is placed well forward and extends little above the level of the head. The internal tuberosity is small. The bicipital groove is undivided and is displaced to the inner side by the extension forward of the external tuberosity. The distal end bears an oblique trochlear articular surface for articulation with the radius and ulna, the outer part of which is the more extensive and is faintly grooved. The epicondyles are prominent. The coronoid and olecranon fossæ often communicate through a large =supratrochlear foramen=. [Illustration: FIG. 130.—LEFT HUMERUS OF DOG, EXTERNAL VIEW. _a_, Head; _b_, neck; _c_, crest; _d_, external tuberosity; _e_, mark for insertion of infraspinatus tendon; _f_, external condyle; _g_, external condyloid crest; _h_, coronoid fossa; _i_, olecranon fossa. (Ellenberger-Baum, Anat. d. Hundes.) ] [Illustration: FIG. 131.—LEFT RADIUS AND ULNA OF DOG, ANTERO-EXTERNAL VIEW. _A_, Radius; _B_, ulna; _a_, groove for tendon of extensor carpi radialis: _b_, groove for common extensor tendon; _c_, proximal articular surface of radius; _d_, olecranon; _e_, beak (proc. anconeus) of ulna; _f_, semilunar notch; _g_, coronoid process; _h_, facet for radius; _i_, groove for lateral extensor tendon; _k_, groove for tendon of extensor carpi obliquus. (Ellenberger-Baum, Anat. d. Hundes.) ]