224 SHOULDER-GIRDLE AND BREAST-BONE. 



the glenoid cup is shallow ; the clavicle (cl.) is stout and sigmoid ; it has drumstick-shaped 

 ends formed of hyaline cartilage ; these are the remnants of a rod primarily developed quite 

 independent of the clavicles. The meso-scapular segment (fig. 10, m. sc. s.) is attached by 

 fibrous tissue to the acromion (ac.), and a synovial cavity has commenced at this part; at the 

 other end the cartilage has been cleft into two segments : one, the prse-coracoid (fig. 11, p. cr.), 

 has become hyaline cartilage, and is in close contact with the bony clavicle ; whilst the distal 

 piece (o. st.) has become fibro-cartilage. The Sternum, at this stage, has not become segmented 

 from the first rib (s. r. 1) on the right side ; the manubrium (p. st.) is cut off, by fibrous tissue, 

 from the meso-sternum (m. st.), the two halves of which are still distinct (st. f.) ; the xiphoid 

 region (x.) is also double, and is pinched, in some degree, off from the meso-sternum. Ossifi- 

 cation is advancing along the vertebral ribs (v. r.), but all the rest is soft. At the next stage 

 (fig. 12, an embryo five inches six lines in length, one-and-a-half diameter) the scapular shaft is 

 spreading ; the prse- scapular region (p. sc.) is becoming wider, and the coracoid (cr.) is more 

 hooked inwards. A synovial cavity is now clearly seen between the acromion (ac.) and the 

 meso-scapular segment (in. sc. s.) ; this latter part is much ossified by the clavicle (cl.), and is 

 now a mere cap of cartilage ; the prse-coracoid, however (p. cr.), is much enlarged, and has acquired 

 its own endosteal centre, whilst the omosternal meniscus (o. st.) has become more differentiated. 

 The Sternum has lost its primordial fissure ; a band of fibrous tissue separates the manubrium 

 from the body of the Sternum ; a notch on each side marks out the xiphoid (x.) ; and here, in 

 this specimen, the left first rib is continuous with the manubrium (p. st.). 



In the next stage (fig. 13, twin foetus of the seventh month, one-and-a-half diam.), the ossifying 

 prae-coracoid (p. cr.) and the meniscoid omosternum (o. st.) are well shown ; the first " pleti- 

 rosteon " has appeared in the manubrium (p. st.), and the second in the first division of the meso- 

 sternum (m. st.). The manubrial centre is shown in section in fig. 14 (two diameters), and it 

 is seen to be endosteal. At birth (fig. 15, three-quarters of natural size) these two centres 

 are much extended, and three pairs of meso-sternals have arisen behind them. In the adult 

 skeleton of the Boschman (Hunterian Museum) the primordial fissure is interruptedly persistent ; 

 between the fourth and fifth sternals " fontanelles " may be seen. The xiphoid process (x.) is 

 very variable in form (see figs. 13 and 15) ; it is the last region to ossify. The primary scapular 

 shaft is supplemented, as is well known, by two epiphyses in the acromion, another in the 

 coracoid, one along the supra-scapular border, and a fifth at the posterior (= inferior) angle. 



Note. At the last hour Dr. Giinther has put into my hands his valuable Paper on that unique 

 Lacertian Hatteria (see 'Phil. Trans./ 1867, part 2, pp. 1 35, Plates 1 3). In this type 

 Dr. Gunther has discovered retral costal appendages (PI. 2, fig. 17), like those so well known in Birds ; 

 and, what is still more interesting and important, he describes and figures a large series of abdominal 

 splints, exactly answering to those of the extinct Plesiosaurus. There is an azygous series along the 

 mid-line, each bone bent on itself at an obtuse angle ; and, articulating with the ends of these, a 

 symmetrical series (PI. 2, fig. 26) ; so that this creature has three splints where the Crocodile has only 

 two. Dr. Gunther confounds the paired splints of the Crocodile with the abdominal ribs of Chamceleo 

 and Polychrus (p. 14). The parts in Hatteria that correspond with the abdominal ribs of the 

 Chamseleon are the outspread cartilages that terminate the floating ribs (PI. 2, fig. 20) ; occasionally, 

 the floating ribs meet at the mid-line, as in Chamceleo and Polychrus (p. 14). 



