TEE ANTERIOR LIMBS. 



101 



Arm. 



Fig. 62. 



This region has only one bone, the humerus. 



Humerus (Figs. 62, 63). 



The humerus is a long single bone, situated between the scapula and the bone 

 of the forearm, in an oblique direction downwards and backwards. Like all the 

 long bones, it offers for study a bodt/ and two extremities. 



Body. — The body of the humerus looks as if it had been twisted on itself from 

 within to without in its superior extremity, and from 

 without to within at the opposite end. It is irregularly 

 prismatic, and is divided into four faces. The anterior 

 face (Fig. 62), wider above than below, has in its middle 

 and inferior portions some muscular imprints. The pos- 

 terior, smooth and rounded from one side to the other, 

 "becomes insensibly confounded with the neighbouring 

 faces. The external is excavated by a wide furrow, which 

 entirely occupies it, and turns round the bone obliquely 

 from above to below and behind to before ; it is to the 

 presence of this channel that the humerus owes its ap- 

 parent twist, and it is in consequence designated the /?/rrow 

 of torsion (or inusculo-spiral groove) of the body of the 

 humerus. 



This furrow is separated from the anterior face by 

 a salient border — the deltoid ridge, which ends inferiorly 

 above the coronoid fossa, and superiorly, towards the 

 upper third of the bone, by the imprint, or deltoid (or 

 external) tuberosity. This is a roughened, very prominent 

 eminence, flattened before and behind, and inclining to- 

 wards the furrow of torsion ; by its superior extremity, 

 it gives origin to a curved line which is carried backwards 

 to join the base of the articular head. Near the inferior 

 extremity, backwards and outwards, is seen the posterior 

 deltoid ridge, which separates the latter from the posterior 

 face of the bone. The internal face of the body of the 

 humerus, rounded from side to side, is not separated from 

 the anterior and posterior faces by any marked line of 

 demarcation. It offers, near its middle, a depressed 

 scabrous process (the internal tuberosity) for the insertion of 

 the teres major and latissimus dorsi muscles. Towards its 

 inferior third it shows the nutrient foramen of the bone. 



Extremities. — These are distinguished into superior and 

 inferior. Both are slightly curved — the first backwards, 

 the second forwards— a disposition which tends to give to the humerus the form 

 of an S. 



The superior extremity is the most voluminous, and has three thick eminences — 

 a posterior, external, and internal. The first constitutes the head of the humerus. 

 It is a very slightly detached articular eminence, rounded like the segment of a 

 sphere, and corresponding with the glenoid cavity of the scapula, which is too 

 «mall to receive it entirely. The external eminence — named the trochiter, large 



ANTERO-EXTERNAL VIEW 

 OF RIGHT HUMERUS. 



1, Trochlear or bicipital 

 ridges ; 2, external or 

 deltoid tuberosity ; 3, 

 head or articular sur- 

 face ; 4, external tuber- 

 cle ; 5, shaft or body 

 with its twisted fur- 

 row; 6, 7, articular or 

 trochlear condyles; 8, 

 uluar fossa with a sul- 

 cus; 9, fossa for the 

 insertion of the exter- 

 nal lateral ligament. 



