CLAVICLE. 199 



in the first cartilage sooner than in the others ; and in men more frequently, 

 and at an earlier period of life than in women." 



Attachment of Muscles. The Subclavius, Sterno-thyroid, Pectoralis Major, 

 Internal Oblique, Transversalis, Kectus, Diaphragm, Triangularis Sterni, Inter- 

 nal and External Intercostals. 



OF THE EXTKEMITIES. 



The Extremities, or limbs, are those long-jointed appendages of the body, 

 which are connected to the trunk by one end, and free in the rest of their ex- 

 tent. They are four in number : an upper or thoracic pair, connected with the 

 thorax through the intervention of the shoulder, and subservient mainly to 

 tact and prehension ; and a lower pair, connected with the pelvis, intended for 

 support and locomotion. Both pairs of limbs are constructed after one common 

 type, so that they present numerous analogies ; while at the same time certain 

 differences are observed in each, dependent on the peculiar offices they perform. 



OF THE UPPER EXTREMITY. 



The Upper Extremity consists of the Arm, the Forearm, and the Hand. Its 

 continuity with the trunk is established by means of the Shoulder, which is 

 homologous with the innominate or haunch bone in the lower limb. 



The Shoulder is placed upon the upper part and side of the chest, connect- 

 ing the upper extremity to the trunk ; it consists of two bones, the Clavicle, 

 and the Scapula. 



THE CLAVICLE. 



The Clavicle (clavis, a "key"), or collar-bone, forms the anterior portion of 

 the shoulder. It is a long bone, curved somewhat like the italic letter/, and 

 placed nearly horizontally at the upper and anterior part of the thorax, imme- 

 diatelv above the first rib. It articulates by its inner extremity with the upper 

 border of the sternum, and, by its outer extremity, with the acromion process 

 of the scapula ; serving to sustain the upper extremity in the various positions 

 which it assumes, whilst, at the same time, it allows of great latitude of motion 

 in the arm. The clavicle is nearly horizontal. It presents a double curvature, 

 when looked at in front ; the convexity being forwards at the sternal end, and 

 the concavity at the scapular end. Its outer third is flattened from above down- 

 wards, and extends in the natural position of the bone, from the coracoid pro- 

 cess to the acromion. Its inner two-thirds are of a cylindrical form, and extend 

 from the sternum to the coracoid process of the scapula. 



External or Flattened Portion. The outer third is flattened from -above down- 

 wards, so as to present two surfaces, an upper and a lower ; and two borders, 

 an anterior and a posterior. The upper surface is flattened, rough, marked by 

 impressions for the attachment of the Deltoid in front, and the Trapezius be- 

 hind : between these two impressions, externally, a small portion of the bone 

 is subcutaneous. The under surface is flattened. At its posterior border, where 

 the prismatic joins with the flattened portion, is a rough eminence, the conoid 

 tubercle ; this, in the natural position of the bone, surmounts the coracoid pro- 

 cess of the scapula, and gives attachment to the conoid ligament. From this 

 tubercle, an oblique line, occasionally a depression, passes forwards and out- 

 wards to near the outer end of the anterior border ; it is called the oblique line, 

 and affords attachment to the trapezoid ligament. The anterior border is con- 

 cave, thin, and rough ; it limits the attachment of the Deltoid, and occasionally 

 presents, near the centre, a tubercle, the deltoid tubercle, which is sometimes dis- 

 tinct in the living subject. The posterior border is convex, rough, broader than 

 the anterior, and gives attachment to the Trapezius. 



