174 



the presternum is smooth and concave from side to side; behind, 

 it rises in the mid-line into a small eminence, which supplies most 

 of the before-mentioned facet for the mesosternum, the remainder 

 being furnished by the root of the keel. 



The six mesosternal segments (fig. 6 i) are compressed from side 

 to side, and slightly expanded at each end, where they articulate 

 with one another. 



The first two are of equal length, and each is nearly as long as 

 the presternum, but the four segments which succeed are only about 

 half as long as these. The sternal ribs abut on the junctions of 

 the mesosternal segments, that of the second meeting the points 

 of contact of the first and second. In the case of the second, 

 third and fourth the abutment is directly at the side of the 

 mesosternal junction ; while in the case of the fifth, sixth and 

 seventh the ends of the sternal ribs lie ventral to the mesosternum, 

 and almost meet one another in this position. 



The ziphisternum (fig. 7) is a slender bony rod nearly as long 

 as the first segment of the mesosternum, having for its terminal 

 portion a flat cartilaginous expansion. 



THE SHOULDER GIRDLE. 



(PI. YIIL, figs. 1, la, lb and 3b). 



The scapula is narrow for its inferior, or, in its natural 

 position in the animal for its anterior, two-thirds, but wide 

 superiorly (or posteriorly), owing to the rapid divergence of 

 the glenoid and coracoid borders at their posterior ends. The 

 suprascapular border is thus of considerable extent, and the 

 angles at its junction Avith the glenoid and coracoid borders, res- 

 pectively, form prominent hook-like process which turn forwards" 

 and inwards (fig. 1). 



The mesoscapular spine is well developed (fig. 1 s). Rising from 

 almost the whole length of the bone, it is carried forward to form a 

 long acromial process, leaving a deep notch between this and the 

 scapular neck ; it is besides much inflected, so as to overhang the 

 postscapular fossa. 



The postscapular fossa, much wider than the prescapular, gives 

 origin to a well-developed second spine which lies nearer to the 

 glenoid border than to the mesoscapular spine. Near the glenoid 

 cavity it runs almost flush with the glenoid border — indeed, at 

 that part one might describe the glenoid border itself as being 

 turned up to form the second spine, (fig. 1 gb. ss). The free edge of 

 this second spine in parts so nearly approaches the edge of the 

 overhanging mesoscapular spine as almost to convert the groove 

 between them into a tube ; as it is, it is an exceedingly deep canal 

 (figs. 1., la., lb.) Approaching the scapular neck, this second 

 spine still further rises into a marked flat process, (fig. 1 ;;) which 



