ARTICULATIONS OF THE ANTERIOR LIMBS. 147 



inferior moiety a fihro-cartilnginous cnp whicli is fixed on the ulna and radius, and unit. -.1 

 in front to the annular ligament of tin- superior radio-ulnnr joint. Thi-eap. with tli(! last- 

 named ligament, completis the osteo-fibrous ring in which the, superior extremity of the 

 rail ins turns. Tin- internal lateral ligament is inserted liy two very short fasciculi into 

 the ulna ami inner side of the head of the radius. A third fasciculus, dee|>er and median, 

 nuieli more develojx-d than the first, and covered by the inferior insertion of the flexors 

 >f the fore-arm, descends between the radius and ulna to tho posterior face of tlio 

 former, and is there inserted near the inferior attachment of the external ligament, 

 which it appears as if alniut to join. 



In Man. the elbow articulation is formed nearly on the same plan as that of the Dog 

 t . The radius and ulna move together when the fore-arm is flexed and extended 

 on the linnierus. 



3. Radio-ulnar Articulation. 



Articular surfaces. Tho two bones of tho fore-arm correspond by 

 diarthrodial and synartlirodial surfaces. 



a. Tho diarthrodial surfaces consist of four undulated, transversely 

 elongated facets, two. of which are radial and t\vo ulnar. The first border, 

 posteriorly, the great articular surface forming the elbow joint ; the second 

 : nated beneath the sigmoid notch. 



/>. The synartlirodial surfaces are piano and roughened, and are also two 

 en each bone: one, superior, extends below the diarthrodial facets to the 

 radio-ulnar arch ; tho other, inferior, more extensive, occupies all the 

 anterior face of tho ulna from this arch , on tho radius it forms a very 

 elongated triangular imprint which descends to the lower fourth of the bone. 

 See pages 75, 76. 



Mode of union. Two iuterosseous and two peripheral ligaments. 



a. Tho interosseous ligaments, interposed between the synarthrodial 

 surfaces, are composed of extremely short white fibres passing from one to 

 the other surface, and which are endowed with a very remarkable power 

 of resistance. The inferior always ossifies a long time before the animal 

 is full grown : a circumstance which caused the older veterinary anatomists 

 to describe, and with some show of reason, tho radius and ulna as a single 

 bone. Ossification of tho superior ligament is very rare. 



6. The peripheral bands are bundles of arciform fibres which, from the 

 beak of the olecranon to the radio-ulnar arch, leave tho lateral faces of 

 ilna to pass, some inwards, others outwards, to the posterior faco 

 of tli<: radius. Tho fibres of the external ligament are confounded with tho 

 external huraero-nulial ligament. The internal fibres are united to tho 

 internal humero-radial ligament, and to the small uluar tendon belonging 

 t-i the short flexor of the fore-arm. Analogous fibres are found beneath tho 

 radio-ulnar arch; but they are much shorter and less apparent. (This is 

 tin < j-fernal transverse radio-ulnar ligament of Leyh.) 



Movements. Very obscure in youth ; nearly null when consolidation of 

 the two bones takes place. 



In the Ox, ossification of the superior interosaeous ligament is constant at adult 

 age. 



:hc Dog and Cat, wo have already seen (p. 87) that the radius and ulna are not 



:iier, but remain indej>endent during life. They are uniie.l in their 



middle portion by an iuterosseous ligament, and join by diurthn-s-i* at their two 



mities. These animals therefore exhibit: 1, An interottrout liijnmrnt ; 2, A 



>r radi'o-ulnar artifiilntinn ; 3, An inferior radio-ulnur nrtirnlnllnn. 

 Interotteon* li,jni,i> ut. It is composed of very resisting white tilms. attached by 

 tin ir extremities {> th-- l-"dii -s i-f the bones. Notwithstanding their whortncss, they aro 

 loose enough to allow movements taking place lictween the rodio-nlmir articulations. 

 Superior radio-ulnnr articulation. This is a trochoid articulation, which only allow- 

 .-UN of rotation or pivoting. 



L 2 



