8 SHOULDER-GIRDLE AND BREAST-BONE. 



The oblique and vertical parts of the posterior margin of the scapula meet at less than a right 

 angle, so that this part projects upwards (fig. 2, sc.). Half-way down, this rapidly widening 

 scapula breaks into three bars ; and these form three regions, namely, the " prse-," " meso-," and 

 " post-scapular " regions ; the two outer are each twice the breadth of the inner. These are 

 differentiated by that process in the metamorphosis of the primordial skeleton which may be 

 termed " cleavage ;" and if this process had been perfect in the Skate, there would have been 

 a division, vertically, into parallel rays ; besides the transverse cleft which separates the supra- 

 scapula from the scapula. When, however, this process is arrested, at one end we have a 

 "notch;" when at both ends we have a " fenestra,'' for this closed space does not continue a 

 mere chink ; but the expansion by growth of the cartilage causes it to become' a more or less 

 broad " window" in the cartilaginous plate : it is generally oval in shape. Three such " fenestoe" 

 are shown in fig. 2 ; the front one belongs principally to the scapula, and also to the coracoid (cr.) 

 beneath this is the " coraco-scapular fenestra" (c. s. f.). Behind this there is a somewhat wider 

 space, which belongs wholly to the scapula, being above the glenoid facets; this is the " scapular 

 fenestra" (sc. f.). Below this there is a rather strong bar of cartilage which connects the second 

 and third glenoid facets ; it is almost horizontal, but dips a little behind : this may be called the 

 " glenoid commissure" (gl.). Below this rod there is a somewhat smaller, narrow-oval fenestra, 

 which belongs wholly to the coracoid region : this is the " coracoid fenestra" (cr. f.). The outer 

 face of the scapula is scooped (fig. 2) ; and whilst the middle glenoid facet (fig. 1, gl.) projects 

 laterally to nearly the same line as that in front (gl. 2), the posterior facet (gl. 3), like the rest of 

 the hinder part of the Shoulder-girdle, projects to some considerable distance further outwards 

 (figs. 1, 2, and 3, gl. 3). Where the scapula and coracoid run insensibly into each other in the 

 glenoid region they are both at their greatest breadth ; the latter part (cr.) narrows rapidly to its 

 lowest part (fig. 2). The extension, to some slight degree, of the coraco-scapular fenestra (c. s. f.) 

 into the coracoid region in front, and the presence of a true coracoid fenestra (cr. f.) in the hinder 

 half, makes the coracoid in some degree trifid ; the front part is the " prse-coracoid" (p. cr.) ; the 

 middle bar, which underprops the middle glenoid facet, is the " meso-coracoid " (m. cr.) ; whilst 

 the broad bar which runs up to the hinder glenoid facet is the " post-coracoid/' or " coracoid- 

 proper" (cr.) : all these parts will reappear in the higher classes with more or less distinctness ; 

 and I promise to prove that there is nothing unmeaning in these " fenestrse '' and bars ; and 

 that teleology need not be called in to show the " why and wherefore " of their existence. 

 Each great coracoid is bent upon itself at an acute angle at the eighth of an inch below the 

 transverse coracoid fenestra (figs. 2 4) ; and the cartilage, which is sixteen lines broad at 

 the glenoid region, becomes three lines only where it meets and coalesces with its fellow of the 

 opposite side. 



The union of these two halves is absolute (figs. 3 and 4, e. cr.) ; there is no stoppage of the 

 ossification at the mid-line, and no thinning down of the cartilaginous bar (fig. 4, e. cr.) : the 

 lower part of the Shoulder-girdle is formed by the " epi-coracoids" (e. cr.), here most massive, but 

 reappearing in the higher types as thin-edged, free plates. The great, common epi-coracoid bar 

 is rounded above (fig. 4), somewhat concave at the mid-line and with round thick edges below : 

 the arcuate anterior and posterior outlines of this bar, as it spreads out to lose itself on each side 

 in the upper coracoid region, are very beautiful, and so is the whole arch Nature's own 

 masonry ! 



