200 SHOULDER-GIRDLE AND BREAST-BONE. 



the small pupiform omostcrnal piece, evidently composed of hyaline cartilage. A ligament connects 

 the omosternum with the side of the prae-sternum (p. st.). In the old Ai (Hunt. Mus., No. 2367) 

 the clavicle has dwindled to a small hook, capped with cartilage ; and in default of the acromial 

 connection, it articulates with the coracoid (fig. 14, cl.), whilst the structures at its distal end have 

 degenerated into ligamentous substance. The Sternum in the nearly ripe embryo (fig. 4, from 

 below, two and a half diameters, and figs. 5 and 6, from above, four diameters) is broad above, 

 and very narrow in the remaining part; the pra-sternum (p. st.) is completely segmented from 

 the meso-sternum (m. st.) ; it is only gently rounded in front, but does not project into the cervical 

 region ; it is not in the least segmented from the first costal arch ; and the ectosteal substance of 

 the first pair of vertebral ribs have grown down close upon it. The fore-edge of the meso- 

 sternum is turned down below (fig. 4), and it is somewhat compressed in its narrow part, as are 

 also all the other sternal segments : above (fig. 6) they are somewhat flattened. The sternal ribs 

 are not ossified, nor are they segmented from the ossifying vertebral ribs ; they articulate, by a 

 cavity-joint with their own and with the preceding segment. There are only six meso-sternal 

 pieces in this specimen ; and the last piece is an aborted xiphisternum (x. st.), the keystone of the 

 eighth costal arch. In a half-grown Ai (fig. 10) a large endosteal patch has appeared in the 

 prse-sternum (p. st.), and one on each side of it (s. r. 1) ; these last are the first sternal ribs, connate, 

 as cartilage with the vertebral portion (v. r.), and with the Sternum. In another half-grown Ai 

 a section of the Sternum (fig. 8) shows nine pieces, and the pra>sternal centre is here seen to lie 

 within the cartilage, see fig. 9, p. st., pi. o. 1 ; the next centre has reached the upper surface of the 

 cartilage (pi. o. 2) : between the segments there is a synovial cavity (sy.). I have seen no super- 

 numerary bony centres in any Sternum of the Ai; fig. 12 shows the seventh, eighth, and ninth 

 sternals of the nearly adult individual ; and here may be seen the abortion of the last or xiphoid 

 piece. In the old Ai (fig. 15), whose scapula is shown in figs. 13 and 14, there are two curious 

 irregularities, for the prse-sternum is divided into an anterior large piece, and a very small 

 posterior segment : here the front segment should be the " pro-osteon" (pr. o.), and the other the first 

 "pleurosteon" (pl.o. 1). The cervical beak is more projecting; the right sternal rib is partly segmented 

 off by a fenestra (f.), and the left by a notch (n.) ; and the primary continuous condition is again 

 shown by the anchylosis of all the first arch (s. r. 1 and v. r. 1), and by the coalescence of the 

 vertebral with the sternal ribs (v. r. 5, s. r. 5), in the next four arches. In the Unau the clavicle is 

 larger (figs. 16 and 17 young, figs. 22 and 23 old) ; and the "omosternum" is composed of 

 fibro-cartilage (figs. 17 and 19, o. st.) : this part nearly reaches the manubrium in the young, 

 but in the adult the fibro-cartilaginous segment has deteriorated into a mere ligament. The 

 cervical part of the prae-sternum is long and emarginate in the Unau (figs. 16 and 23) ; it is more 

 carinate below, and in the old specimen (fig. 23) the second pair of sternal ribs have lost their 

 connection with their own segment, and altogether articulate with the manubrium. In fig. 16 

 the sternal joints are shown as a horizontal section, the flattish upper surface being sliced away, 

 and thus the very great distinctness of the segments is better shown, reminding the observer of 

 the " metasternals" of the Chamaeleon, and of Polychrus. There are twelve of these altogether, 

 and the last (s. 12) is so completely surrounded by the thirteenth sternal ribs, that it can scarcely 

 lie called a "xiphisternum." There is no segmentation of the rib itself; and in old age the 

 nine foremost costal arches suffer anchylosis of the vertebral with the sternal parts. 



In the Pangolins (Plate XXII, figs. 1, 2, 8, 9, 13) the scapula is broad, and the anterior 

 margin passes gently into the superior, as in the Platypus, but to a less degree. The supra- 



