80 THE SKELETON OF THE HORSE 



teriorly the groove extends upward considerably above the rest of the articular 

 surface and reaches the olecranon fossa, and this part articulates with the semilunar 

 notch of the ulna. The external condyle (Condylus laterahs) is much smaller and 

 is placed somewhat lower and further back, giving the extremity an oblique ap- 

 pearance ; it is marked by a wide shallow groove. The coronoid fossa (Fossa coro- 

 noidea) is situated in front above the groove on the internal condyle; it furnishes 

 origin to part of the extensor carpi, and external to it is a rough depression from 

 which the anterior or common extensor of the digit arises. Behind and above the 

 condyles are two thick ridges, the epicondyles. The internal or flexor epicondyle 

 (Epicondylus medialis s. flexorius) is the more salient; it furnishes origin to flexor 

 muscles of the carpus and digit, and presents internally a tubercle for the attach- 

 ment of the internal lateral ligament of the elbow joint. The external or extensor 

 epicondyle (Epicondylus lateralis s. extensorius) bears externally the external 

 supracondyloid crest (Crista condyloidea lateralis), which forms here the outer 

 boundary of the musculo-spiral groove, and gives origin to the extensor carpi. 

 Below this is a rough excavation in which the external lateral hgament is attached. 

 The lower border of the epicondyle gives attachment to the flexor carpi externus. 

 Between the epicondyles is the deep olecranon fossa (Fossa olecrani). 



Development. — The humerus ossifies from six centers, viz., three primary 

 centers for the shaft and epiphyses, and three secondary centers for the external 

 tuberosity, the deltoid tuberosity, and the internal condyle. The proximal end 

 fuses with the shaft at about three and one-half years, the distal at about one and 

 a half years of age. 



THE RADIUS 



The radius is much the larger of the two bones of the forearm in the horse. 

 It extends in a vertical direction from the elbow, where it articulates with the hum- 

 erus, to the carpus below. It is gently curved, the convexity being anterior. It 

 consists of a shaft and two extremities. 



The shaft (Corpus radii) is curved in its length, somewhat flattened from before 

 backward, and expanded at its ends. It presents for description two surfaces and 

 two borders. The anterior surface (Facies dorsalis) is smooth, slightly convex in 

 its length, and rounded from side to side. The posterior surface (Facies volaris) 

 is correspondingly concave in its length and is flattened in the transverse direction. 

 At its upper part there is a smooth shallow groove, which concurs witli the ulna in 

 the formation of the interosseous space of the forearm; the nutrient foramen is 

 in the lower part of this groove. Below this there is in the young subject a narrow, 

 rough, triangular area to which the ulna is attached by an interosseous ligament; 

 in the adult the two bones are fused here. A variable rough elevation below the 

 middle of the surface and close to the internal border gives attachment to the 

 superior check ligament. The internal border (Margo medialis) is slightly con- 

 cave in its length and is largely subcutaneous; at its proximal end there is a 

 smooth area on which the tendon of insertion of the brachialis muscle lies, and a 

 small rough area just below gives attachment to that muscle and the long internal 

 lateral ligament of the elbow-joint. The external border (Margo lateralis) is more 

 strongly curved, but presents no special features. 



The proximal extremity or head (Capitulum radii) is flattened from before 

 backward and wide transv(n'sely. It presents an articular surface (Fovea capituli) 

 which corresponds to that on the distal end of the humerus; it is crossed by a 

 central sagittal ridge, which has a synovial fossa on its posterior part, and ends in 

 front at a prominent lip, the coronoid process (Processus coronoideus). Just 

 below the posterior border there are two {'on('a^'(> facets for articulation with the 

 ulna, and between these and the interosseous space is a quadrilateral rough area 

 at which the two bones are united by an interosseous ligament. At the inner side 



