160 



EXTREMITY. 



At die junction of the middle and inferior 

 thirds we notice a very slight and superficial 

 groove passing downwards and inwards, and 

 very much resembling what one would ima- 

 gine might be produced by an attempt to twist 

 the bone while yet in a yielding condition, the 

 inferior third having been twisted inwards and 

 the two superior thirds outwards. This groove 

 indicates the spiral course from above down- 

 wards and from without inwards of the musculo- 

 spiral or radial nerve. Below this groove is the 

 inferior third of the humerus, the anatomical 

 characters of which are very distinct from those 

 of the remaining parts of the bone. A pro- 

 minent and rounded ridge, continuous with 

 that already noticed in connexion with the 

 greater tuberosity, passes vertically down in 

 front of it; from each side of this ridge a 

 smooth surface inclines backwards, forming 

 an inclined plane on each side of it, the ex- 

 ternal being larger and more distinct than the 

 internal. 



The posterior surface of the upper part of 

 this portion is flat and very smooth. As the 

 bone descends it expands considerably late- 

 rally, so as to present in front a broad surface 

 slightly convex from side to side, bounded on 

 either side by prominent edges, continued from 

 the edges of the inclined planes above de- 

 scribed. Each edge terminates in a pro- 

 minence, the inner one being the largest ; the 

 inner edge itself being thicker, more pro- 

 minent, and describing a slight curve as it 

 descends. The posterior surface is limited 

 below by a deep depression, to be further de- 

 scribed hereafter. Thus, by its gradual expan- 

 sion laterally, the inferior portion of the hu- 

 merus, being about one fifth of the entire 

 length of the bone, has a triangular figure, the 

 base being formed by the inferior articular ex- 

 tremity of the bone. 



The whole shaft of the humerus is com- 

 pletely clothed with muscle. We have already 

 indicated the place of insertion of the deltoid 

 muscle on the outer surface of the bone; all 

 that portion of the outer and anterior surface 

 below the deltoid ridge, and for a little way 

 on each side of its inferior extremity, is co- 

 vered by the brachiaeus anticus muscle. In- 

 ternal to the bicipital groove, on the inner 

 surface of the humerus, about its middle, the 

 coraco-brachialis muscle is inserted. The ex- 

 ternal edge below the spiral groove affords 

 attachment to the brachiams anticus, supinator 

 longus, extensor carpi radialis longior, and the 

 triceps muscles. 



The internal edge below the insertion of 

 the coraco-brachialis has the brachiaeus anticus 

 and triceps muscles inserted into it, and both 

 edges afford insertion to intermuscular apo- 

 neuroses, which separate the muscles con- 

 nected with the anterior from those on the 

 posterior part of the bone. The posterior sur- 

 face is completely covered by the triceps mus- 

 cle, excepting in the line which corresponds 

 to the groove already referred to, in which the 

 radial nerve and musculo-spiral artery pass. 



The foramen for the nutritious artery is found 

 upon the internal surface at the inferior ex- 



tremity of its middle third ; the direction of 

 the canal is downwards ; sometimes this fora- 

 men exists upon the external, or upon the in- 

 ternal surface. 



The inferior extremity of the humerus is 

 terminated by an articular cylinder, which pro- 

 jects into a plane anterior to that of the shaft 

 of the bone, (processus cubitatis). This cy- 

 linder is placed transversely, but in transverse 

 extent it falls short of the widest part of the 

 inferior third of the }iumerus. Various de- 

 pressions and elevations are marked upon the 

 surface of this cylinder. Proceeding from 

 without inwards, we notice a convexity or 

 rounded head, limited externally by the mar- 

 gin of the cylinder and internally by a groove, 

 which passes in a curved direction from before 

 backwards, the concavity of the curve corres- 

 ponding to the rounded head. This head is 

 properly denominated the external condyle of 

 the humerus; it articulates with a cavity on 

 the head of the radius ; the anatomist should 

 notice that the axis of this head passes in a 

 direction downwards and forwards. On the 

 anterior surface of the humerus immediately 

 above this head, we observe a slight and very 

 superficial depression which receives the edge 

 or lip of the cavity of the radius, when the 

 forearm is in a state of complete flexion. 

 Internal to the groove which bounds the con- 

 dyle on the inner side, we have a pulley-like 

 surface, which is destined for articulation with 

 the ulna. The concavity which forms the cen- 

 tral part of this pulley is deep, but deeper and 

 wider behind than before; its anterior ex- 

 tremity terminates in communicating with an 

 oval depression on the anterior surface of the 

 bone (Jbvea anterior minor), which in flexion 

 of the forearm receives the anterior projecting 

 angle of the coronoid process of the ulna ; 

 the posterior extremity terminates in a similar 

 depression, (fovea. posterior v. sinus maximus,) 

 but a much deeper one, and of greater dimen- 

 sions generally, occupying, in short, nearly the 

 whole posterior surface of the bone; this de- 

 pression receives the olecranon process of the 

 ulna, when the elbow-joint is in extension. 

 The trochlear concavity, in passing from before 

 backwards, takes a curved direction, so that its 

 posterior extremity is much nearer the external 

 part of the articular cylinder than the anterior. 

 This has an important influence on the direc- 

 tion of the motions of the forearm. These 

 two depressions are separated from each other 

 by a thin osseous lamina, almost transparent. 

 We sometimes meet with instances in which 

 this lamina is perforated in consequence of a 

 defect of ossification ; and Meckel states that 

 he has found this perforation more frequently 

 in the bones of Negroes and Papuas than in 

 those of the superior races of mankind. It is 

 the permanent condition of many pachydermata, 

 rodentia, carnivora, and quadrumana. On the 

 inside the trochlear concavity is bounded 

 by a thick and projecting lip, which, when the 

 bone is placed at right angles with a horizontal 

 plane surface, descends lower down than any 

 other part, so that this part comes in contact 

 with the plane surface, while the remaining 



