MAMMALS. 203 



Families, the scapula (Plate XXIII, fig. 17, one third nat. size) is high, angular, oblique, rather 

 broad above and narrow below ; the supra-scapula (s. sc.) is a mere selvedge of cartilage ; the 

 prae-scapula (p. sc.) projects considerably forwards, and ends, halfway down, in an obtuse, 

 rounded angle. The meso-scapula (m. sc.) is developed into a strong, straight crest, which 

 becomes very broad, and bilobate below ; this is the acromion (ac.) ; its " metacromial process" 

 (m. ac.) is turned backwards and upwards, but the primary bar is in a line with the spine. The 

 post-scapula (sc.) bulges, and then contracts, so that the scapula has a sort of second neck of 

 moderate width. The coracoid (cr.) is a short, curved, crumpled process ; it is separated from 

 the prse-scapula by a very shallow, open notch. The clavicle (cl.) has used up its correlated 

 cartilages ; it is a strong, curved club, being narrow and rounded above, and very swollen where 

 it articulates with the manubrium. This latter part (fig. 18, p. st.) is trowel-shaped, the first 

 sternals articulating with the " handle " the rest of the joints are one third the width of the 

 clavicular part of the prse-sternum ; they are very uniform, oblong, flat (see fig. 19), the lower 

 surface being of less extent than the upper ; they are thoroughly ossified, have no additional ossicles, 

 at least none in old age, and articulate by a fibrous septum which seems to possess no cavity. 

 The xiphisternum (fig. 20, x.) spreads but little at the end, and has a small unossified margin. 

 The vertebral ribs (v. r.) are not segmented from the sternals (s. r.), and these latter are partially 

 ossified endosteally : there is no " costa intermedia." 



In Cyclothurm didactylus, which represents the next Family (Plate XXII, figs. 18 20, one and 

 a half diameter; fig. 21, six diameters ; and fig. 22, three diameters) the scapula, like the rest of 

 the skeleton, is much more densely ossified than in the Aard-vark, and the supra-scapular region 

 (fig. 18, s. sc.) is completely ossified continuously with the rest of the bone. The whole blade is 

 broader, the prse-scapula (p. sc.) reaching lower down, and ending in an acute angle ; thus the 

 " notch " is more clearly defined. The spine (m. sc.) is thick, bulges backwards, and is continuous 

 with the coracoid, distally, so that there is no notch between it and the neck of the bone. The post- 

 scapula (sc.) projects considerably behind, and a second crest arises from it sub-marginally ; the 

 coracoid (cr.) is but ill-defined, and is small ; the acromion (ac.), which overrides it, is oblong and 

 rounded. The clavicle (cl.) is of moderate size, and is gently curved ; it has but little cartilage 

 (m. sc. s.) above, but more below (fig. 21, p. cr.) ; and the omosternum (o. st.) has a large bony 

 nucleus in it above, and below forms a sort of second, pedate segment. The lower part of the thorax 

 is intensely ossified ; and there is no sign, in the adult, of subsidiary osseous centres. The Sternum 

 (fig. 18) is segmented in front, after the fashion described in the old Ai (Plate XXI, fig. 15), for 

 the manubrium has a small hinder segment, which helps to carry the second costal arch, and a large 

 trilobate segment in front, which is in relation to the " omosternum," besides articulating with 

 the first costal arch ; this arch does not divide into a sternal and a vertebral portion (Plate XXI 

 fig. 18, p. st., v. r. 1). Here the first bone is the " pro-osteon," and the second the first "pleur- 

 osteon ;" there are six more of this category in the meso-sternum ; and a long, stout, styliform 

 xiphoid (x.), which is somewhat oval in section, has a well-finished, long " metosteon," and a small 

 terminal arrested bony centre. From what I have seen in embryo Armadilloes, I have no doubt 

 concerning the endosteal character of the sternal pieces and sternal ribs in their early condition. 



Each sternal segment appears to have been perfectly cleft from its successor, so as to form a 

 synovial cavity; and a cavity exists between the vertebral and sternal ribs (fig. 22, s. r.,v. r., sy.). 

 The sternal pieces are high (see fig. 20), compressed below (fig. 19), and rounded above (fig. 18); 

 the sternal ribs articulate with them by an oval condyle, these segments being compressed below 



