72 RIBS. 



lunaris), and narrow at its junction with the middle piece. At each 

 superior angle is a deep articular depression (incisura clavicularis) for 

 the clavicle, and on either side two notches, for the articulation of the 

 cartilage of the first rib, and one half of the second. 



The middle piece or body, considerably longer than the superior, is 

 broad in the middle, and somewhat narrower at each extremity. It 

 presents at either side six articular notches, for the lower half of the 

 second rib, the four next ribs, and the upper half of the seventh. 

 This piece is sometimes perforated by an opening of various magnitude 

 resulting from arrest of development. 



The inferior piece (ensiform or xiphoid cartilage) is the smallest of 

 the three, often merely cartilaginous, and very various in appearance, 

 being sometimes pointed, at other times broad and thin, and at other 

 times again, perforated by a round hole, or bifid. It presents a notch 

 at each side for the articulation of the lower half of the cartilage of the 

 seventh rib. 



Development. By a variable number of centres, generally ten, 

 namely, two for the manubrium; one (sometimes two) for the first 

 piece of the body, two for each of the remaining .pieces, and one for 

 the ensiform cartilage. Ossification commences towards the end of the 

 fifth month in the manubrium, the two pieces for this part being 

 placed one above the other. At about the same time the centres for 

 the first and second pieces of the body are apparent ; the centres for 

 the third piece of the body appear a few months later, and those for the 

 fourth piece soon after birth. The osseous centre for the ensiform 

 cartilage, is so variable in its advent, that it may be present at any 

 period between the third and eighteenth year. The double centres 

 for the body of the sternum are disposed side by side in pairs, and it 

 is the irregular union of these pairs in the last three pieces of the body 

 that gives rise to the large aperture occasionally seen in the sternum 

 towards its lower part. Union of the pieces of the sternum com- 

 mences from below and proceeds upwards ; the fourth and the third 

 unite at about puberty, the third and the second between twenty and 

 twenty-five, and the second and the first between twenty-five and 

 thirty. The ensiform appendix becomes joined to the body of the 

 sternum at forty or fifty years ; and the manubrium to the body only 

 in very old age. Two small pisiform pieces have been described by 

 Beclard and Breschet, as being situated upon and somewhat behind 

 each extremity of the incisura semilunaris of the upper border of the 

 manubrium. These pre-sternal or supra-sternal pieces which are by 

 no means constant, appear at about the thirty-fifth year. Beclard 

 considers them to be the analogue of the fourchette of birds, and 

 Breschet as the sternal ends of the cervical rib. 



Articulations. With sixteen bones ; viz. with the clavicle and the 

 seven true ribs, at each side. 



Attachment of Muscles. To nine pairs and one single muscle ; viz. 

 to the pectoralis major, sterno-mastoid, sterno-hyoid, sterno-thyroid, 



