STERNUM. 71 



project backwards from the body ; and two lesser cornua, which, ascend 

 from the angles of union between the body and the greater cornua. 



The body is somewhat quadrila- 

 teral, rough and convex on its ante- 

 ro-superior surface, by which it 

 gives attachment to muscles ; con- 

 cave and smooth on the postero-in- 

 ferior surface, by which it lies in 

 contact with the thyro-hyoidean 

 membrane. The greater cornua are 

 flattened from above downwards, 

 and terminated posteriorly by a 



tubercle ; and the lesser cornua, conical in form, give attachment to 

 the stylo-hyoid ligaments. In early age and in the adult, the cor- 

 nua are connected with the body by cartilaginous surfaces and liga- 

 mentous fibres ; but in old age they become united by bone. 



Development. By five centres, one for the body, and one for each 

 cornu. Ossification commences in the greater cornua during the last 

 month of foetal life, and in the lesser cornua and body soon after 

 birth. 



Attachment of Muscles. To eleven pairs; sterno-hyoid, thyro-hyoid, 

 omo-hyoid, pulley of the digastricus, stylo-hyoid, mylo-hyoid, genio- 

 hyoid, genio-hyo-glossus, hyo-glossus, lingualis, and middle constrictor 

 of the pharynx. It also gives attachment to the stylo-hyoid, thyro- 

 hyoid, and hyo-epiglottic ligaments, and to the thyro-hyoidean mem- 

 brane. 



THORAX AND UPPER EXTREMITY. 



The bones of the thorax are the sternum and ribs ; and, of the 

 upper extremity, the clavicle, scapula, humerus, ulna and radius, bones 

 of the carpus, metacarpus, and phalanges. 



STERNUM. The sternum (fig. 33) is situated in the middle line of 

 the front of the chest, and is oblique in direction, the superior end 

 lying within a few inches of the vertebral column, and the inferior 

 being projected forwards so as to be placed at a considerable distance 

 from the spine. The bone is flat or slightly concave in front, and 

 marked by five transverse lines which indicate its original subdivision 

 into six pieces. It is convex behind, broad and thick above, flattened 

 and pointed below, and is divisible in the adult into three pieces, 

 superior, middle, and inferior. 



The superior piece or manubrium is nearly quadrilateral ; it is broad 

 and thick above, where it presents a concave border (incisura semi- 



* The os hyoides seen from before. 1. The antero-superior, or convex side 

 of the body. 2. The great cornu of the left side. 3. The lesser cornu of the 

 same side. The cornua were ossified to the body of the bone in the specimen 

 from which this figure was drawn. 



