EXTREMITY. 



159 



the humerus to the scapula. The rule seems 

 to be that where the pectoral extremity is chiefly 

 a pillar of support, the aspect of the glenoid 

 cavity is nearly vertically downwards. If free- 

 dom and rapidity of motion be required in 

 addition to strength as a member of support, 

 the trunk being lighter, the scapula is oblique, 

 and consequently the glenoid cavity looks 

 downwards and forwards ; or if the limb be 

 not used to support the trunk, then the aspect 

 of the glenoid cavity is no longer downwards 

 but outwards, as in man. 



Structure. The greatest part of the scapula 

 is composed of very thin almost papyraceous 

 compact substance ; but its processes, and the 

 enlargements at its edges and angles, contain 

 reticular tissue. 



Developement . This bone is developed by 

 six points of ossification ; one for the body, 

 and five supplementary ones, viz. one for the 

 coracoid process, two for the acromion, one 

 for the posterior border of the bone, and one 

 for its inferior angle. The ossification of the 

 body commences about the second month, and 

 the spine appears in the third month as a 

 growth from the posterior surface of the scapula. 



The union of the several epiphyses is not 

 completed till late, and it is not until after the 

 fifteenth year that the ossification is finished. 



The bones of the upper extremity, properly 

 so called, are the humerus, radius, ulna, and 

 bones of the hand. 



Humerus, (os brachii; Fr. Vos du bras; 

 Germ, das Oberarmbein). This is the longest 

 bone of the upper extremity; it is situated 

 between the scapula and forearm, being, as it 

 were, suspended by muscle and ligament from 

 the former. 



Like all long bones, the humerus consists 

 of a shaft and two extremities. The superior 

 extremity is formed by a smooth and rounded 

 convexity, rather less than half a sphere; a 

 slight depression in, or constriction of, the 

 bone, most manifest above, marks the limit of 

 this articular eminence. The eminence is 

 called the head of the humerus ; the constric- 

 tion indicates what is denominated the anato- 

 mical neck of the bone, being that portion 

 which connects the head to the shaft, and 

 analogous to the more developed neck of the 

 thigh-bone. The axis of the neck is but a 

 continuation of that of the head, and passes in 

 a direction from within outwards and down- 

 wards, forming an obtuse angle with the axis 

 of the shaft. The head of the humerus is 

 entirely covered by articular cartilage, and arti- 

 culates with the glenoid cavity of the scapula, 

 to which, however, it obviously does not at all 

 correspond in dimensions. 



The inferior part of the anatomical neck of 

 the humerus is very slightly marked, and is 

 continued in a smooth declivity slightly con- 

 cave from above downwards, into the shaft of 

 the bone. Its superior part is more distinct, 

 and the depth of the groove here seems in a 

 great degree owing to the prominence of two 

 bony protuberances, one situated anteriorly, 

 called the lesser tuberosity, and the other pos- 

 teriorly, denominated the greater tuberosity. 



The lesser tuberosity of the humerus (tuber- 

 culum minus) is somewhat conical in shape, 

 and inferiorly it ends in a smooth, rounded 

 bony ridge (spina tuberculi minoris), which 

 extends downwards and inwards, gradually 

 diminishing in prominence till it is lost in the 

 shaft of the bone at the inner part of its ante- 

 rior surface. The lesser tuberosity gives in- 

 sertion to the tendon of the subscapularis 

 muscle, and the ridge or spine last described 

 forms the anterior and internal boundary of the 

 bicipital groove. 



The greater tuberosity (tuberculum majus, 

 externum s. posterius) forms a considerable 

 prominence on the upper and outer part of 

 the humerus, being the most external part in 

 that situation and easily to be felt under the 

 integuments. Superiorly the constriction cor- 

 responding to the anatomical neck separates it 

 from the head of the humerus ; inferiorly it is 

 continued into and gradually lost in the shaft 

 of the bone at its outer part. A very distinct 

 and prominent ridge ( spina tuberculi majoris) 

 is continued from its anterior extremity down- 

 wards and inclining very slightly inwards, 

 which terminates about the middle of the an- 

 terior surface of the bone, just internal to the 

 deltoid ridge. This ridge is most prominent 

 but smooth in its upper third, in its inferior 

 two-thirds it is less prominent but rough; it 

 forms the posterior boundary of the bicipital 

 groove. On the greater tuberosity three dis- 

 tinct surfaces are marked, to the anterior of 

 which the supra-spinatus muscle is attached, 

 to the middle the infra-spinatus, and to the 

 posterior the teres minor. 



The bicipital groove commences above be- 

 tween the two tuberosities, and passes down- 

 wards and slightly inwards, bounded before 

 and behind by the spines which proceed from 

 those tubercles. This groove, very distinct at 

 its commencement, ceases to be so a little 

 above the termination of the superior third ; 

 in the recent state it is lined by the tendinous 

 expansion of the latissimus dorsi and teres 

 major muscles, and lodges the tendon of the 

 biceps muscle, whence its name. 



From the anatomical neck the bone gra- 

 dually tapers down and becomes more cylin- 

 drical in its form ; this upper portion is, for the 

 convenience of description, distinguished by 

 the name of surgical neck of the humerus. 

 The middle third of the shaft of the bone 

 is prismatic in form ; the external spine 

 which commences at the greater tuberosity 

 is continued down, forming a prominent 

 ridge all down the front of the bone to the 

 termination of its flattened inferior third. The 

 outer part of the middle third of the humerus 

 is remarkable for the rough surface into which 

 the deltoid muscle is inserted, the deltoid ridge, 

 situated nearer the upper than the lower part 

 of this portion, and directed downwards and 

 very slightly forwards. The inner part of the 

 middle third presents a smooth, flattened, and 

 inclined surface, which is continued down in 

 this form to within a very short distance of the 

 inferior extremity of the bone. The posterior 

 surface is rounded and very smooth. 



