MAMMALS. 205 



1. ep., four diameters). Each meso-sternal segment is connected to its fellows by a synovial joint 

 (sy.), and between each two contiguous segments there is an upper and lower synovial cavity for 

 the sternal rib (s. r.), which has the unique character of being two-headed : thus it is curiously 

 imitative of the vertebral rib of the higher Classes with its " capitulum " and " tuberculum." The 

 synovial cavities for the sternal ribs are all bi-form ; and in each of the semi-facets below there 

 is a separate epiphysis : the larger, upper epiphyses are related to both the corresponding sternal 

 joints, and also to the upper head of the sternal rib. 1 



Each sternal segment projects in front, and is emarginate behind (see fig. 24) ; it is also 

 somewhat hourglass-shaped : altogether, there are nine " pleurosteal " centres in each meso-sternal 

 piece. The xiphisternum (fig. 23, x.) is more flattened than in Cyclot/iurus ; it is somewhat 

 spatulate, and has in it, anteriorly, four " metostea :" in old age these become anchylosed 

 (fig. 26). The vertebral and sternal ribs (fig. 22, v. r., s. r.) have neither intermediate piece 

 nor cleft between them ; the latter ossify very slowly by endostosis. 



In the Dasypinae, the endo-skeleton has not suffered in intensity of ossification because of 

 its investment by a most exquisite dermal armour ; but it is like what is seen in the Lepidosteus, 

 which, besides its enamelled coat of mail, has an endo-skeleton stronger by far than that of 

 ordinary Fishes. 



The scapula (Plate XXIII, fig. 1, embryo of Tatusia peba, two and a half diameters; and 

 fig. 12, embryo of Euphractus villosus, two diameters) is in one case (fig. 1), high and angular, 

 like that of the Aard-vark, and in the other (fig. 10) broad and rounded, like that of the Ant-bear. 



In T. peba (fig. 1, s. sc.) the supra-scapular region is well defined, and has a rather straight 

 upper outline ; its angle is rounded in front and hooked behind ; the prae-scapular region (p. sc.) is 

 an almost parallel band of bone ; in front it is but little notched off from the small hooked coracoid 

 (cr.) with its internal osseous centre : there is no " fenestra " in the Dasypoids. The meso- 

 scapular spine (m. sc.) is high, thick below, and sends off a long, flat, forvvardly bent acroimon 

 (ac.) : this is simple in E. villosus (fig. 12), but has a metacromial angle in T. peba (fig. 1). In 

 the adult this angle has grown into a sharp spur (fig. 2, m. ac.), and here we see that the 

 acromion (ac.) has its own ectosteal bony centre, besides its terminal epiphysis. The post-scapula 

 of T. peba is triangular (fig. 1, sc.) ; in E. villosus is much broader, and has a notable second crest 

 (fig. 12, sc.) ; in both the " supra-spinous fossa" is much the smallest. In E. villosus (fig. 12) the 

 "supra-" and " pra-scapular " regions, at their junction, form the projecting upper boundary of 

 the large lunate coraco-scapular notch. The clavicle (cl.) is generally well-developed, and its 

 correlates are perfectly normal (figs. 1 and 10, m. sc. s., p. cr., o. st.) ; in T. peba the omo- 

 sternal moiety (o. st.) is composed of hyaline cartilage, but in E. villosus (fig. 13, o. st. six 

 diameters), it is well segmented off from the prsc- coracoid, but soon degenerates (before birth) 

 into fibro-cartilage : in this species the prae-coracoid segment is of considerable length. 



The coalescence of the sternal moieties and their transverse cleavage are complete before 

 birth (Plate XXIII, figs. 1 and 12) ; the Sternum, as a whole, is greatly dilated both in front 



1 In figs. 24 and 25, from above and laterally, the parts are drawn in a diagrammatic manner ; 

 and the head of the sternal rib in fig. 25 is pushed downwards ; in fig. 24 the upper heads of a pair of 

 sternal ribs are shown attached behind a meso-sternal segment ; but they converge too much in the 

 figure, and lie, in reality, on a much lower plane than the upper surface of the sternal segment. 

 (See fig. 25.) 



