MAMMALS. 



scapula (s. sc.) is a moderately broad headland of persistent cartilage; the prse-scapula (p. sc.) is 

 broader than the post-scapula (sc.), at least in Pholidotus, and especially in the young (fig. 8) ; 

 but the post-scapula is the longest, for it is curved backwards in a falcate manner. The pra- 

 scapula (p. sc.) is separated from the coracoid (cr.) by a small and in the young, shallow 

 notch, and the ectosteal plate is a long while before it covers the lower angle of this 

 region (fig. 8, p. sc.). There is therefore no "fenestra," such as we see in the Sloth, but 

 the " coraco-scapular notch" is typically Mammalian. In the young (fig. 8, m. sc.) there 

 is no "acromion process" to the meso-scapula, but this part has a vertical front margin (fig. 9) : 

 in the adult, in both types, the periosteal growths form a small rudiment of this process (figs. 1, 2, 

 13, ac.). The Pangolins are unique in possessing a true cleft, which partially separates the meso- 

 scapula from the rest of the blade-bone; in Manis this cleft is seen as a fenestra (fig. 13, f.) 

 dividing, in some degree, the "post-" from the "meso-scapula;" but in Pholidotus (figs. 2, 8, 

 9, f.) the cleavage takes place in the root of the spine ; and thus, if perfect, would cut off the 

 crest as a free " meso-scapular ray." In the old Pholidotus (fig. 2) this fenestra is much 

 diminished by means of overgrowing layers of bone. In the old specimens (figs. 1 and 13, sc.) 

 the posterior edge of the scapula is much thickened. The coracoid (figs. 1, 2, 13, cr.) is in its 

 last stage of abortion ; being the merest convexity, and having in it a small endosteal patch. 

 These imbricated types have no clavicles, and the correlated cartilages are absent : the Sternum, 

 however, is developed to an extraordinary degree. 



In the young Pholidotus (fig. 8) the Sternum is seen to be of moderate breadth up to the 

 last two-fifths of the xiphoid region ; the first sternal ribs are already segmented from the side of 

 the "praa-sternum" (p. st. s. r. 1) ; and the latter part is cut off from the " meso-sternum ;" there 

 are then two more meso-sternal clefts, then two are absent, and two more appear, the last of which 

 passes across between the "meso-" and " xiphi-sternum" (x.). A section (fig. 10) shows the other 

 clefts as deep and wide notches in the lower surface of the Sternum, and also the endosteal patches 

 that occupy the first and second meso-sternal joints, and the proximal part of the xiphisternum. 

 The two foremost are " pleurostea," and the last is a " metosteon :" the other meso-sternal 

 regions are dotted with large vascular puncta, preparatory to ossification. Behind the metosteon 

 (fig. 8, m. t. o.) the xiphisternal horns are separated by a fenestra or " fontanelle" (x. f.) ; and 

 when they have closed upon each other again they spread out into a very large, semi-oval, 

 sinuous, eared blade. The four foremost thoracic arches have no cleft between the vertebral 

 (v. r.) and sternal ribs (s. r.), in those that succeed this takes place; but no cavity is formed (see 

 fig. 11, v. r., s. r., f.), but the two elements are tied together by fibrous tissue. 



In the adult Pholidotus (Plate XXII, figs. 1, 3, 4, 5, 6 two thirds nat. size, and three 

 diameters) we see what changes have taken place. There is still very much unchanged cartilage ; 

 but the endosteal patches have grown through, vertically, so as to appear on both the upper and 

 the lower surfaces of the segments : they are, however, arrested laterally, save in the free-edged 

 xiphisternal bone (" metosteon" m. t. o.). All the transverse clefts have become perfect, and are 

 in the highest degree of segmentation, having synovial joint-cavities (sy.). There are three 

 synovial cavities, which are, as far as I have seen, unique ; the first of these is in the transverse 

 cleft between the front and hinder halves of the prse-sternum, between the " pro osteon" (pr. o.) 

 and the first " pleurosteon" (pi. o.) j 1 the other two are between the third and seventh (last) 



1 M. Gegenbauer ('Nat. Hist. Rev./ 1865, p. 548, fig. 2, m.) describes this fibrous cleft in Ccelo- 

 i/enys paca ; the foremost segment is called by him the " median episternal piece" (see also p. 209, infra). 



