528 



ZOOLOGY 



SECT. 



pl.SC 



zygomatic arch remains incomplete. There are, at most, the rudi- 

 ments of post-orbital processes of the frontals. The " pterygoids " 

 develop vertical laminae and form no palatine plates. The 

 ascending ramus and coronoid process of the mandible are both 

 well developed. 



In the American Anteaters and Armadillos, the bones of the 

 fore-limb are short and powerful. The scapula in the Anteaters 

 is broad and rounded ; the anterior border unites with the 

 coracoid process so as to convert the coraco-scapular notch into 

 a foramen, In the middle of the spine there is a triangular 

 process : a ridge on the post-spinous fossa presents the appear- 

 ance of a second spine. The fibres of origin of the subscapularis 

 muscle extend on to the outer surface as far forward as this 

 ridge, so that the part of the outer surface behind the ridge 

 corresponds to a part of the subscapular fossa, which in other 

 Theria is co-extensive with the inner surface. Except in 

 Cycloturus the clavicles are rudimentary. All the carpal bones 

 are distinct. 



In the Armadillos the scapula (Fig. 1141) has an extremely 

 prolonged acromion (acr.), sometimes articulating with the humerus. 



A ridge (sp r .) representing a second 

 spine is present. The clavicle is well 

 developed. The humerus is short and 

 powerful, with well-developed pro- 

 cesses and ridges, and with a foramen 

 above the inner condyle (entepicondylar 

 foramen). The carpus consists of the 

 ordinary eight bones. 



In the Sloths (Fig. 1142) the arm- 

 bones are comparatively long and 

 slender. A coraco-scapular foramen 

 is formed as in the Anteaters. In 

 the three-toed Sloths (Fig. 1143) the 

 acromion (acr.) is at first connected 

 with the coracoid process, but becomes 

 reduced and loses the connection ; in 

 the two-toed Sloth the connection 

 persists. The clavicle (cl.) is not 

 directly connected internally with the 

 sternum ; externally it is connected 

 with the coracoid process a condi- 



observed in no other Mammal. The humerus is very long 

 and slender ; so are the radius and ulna, which are capable of a 

 certain amount of movement in pronation and supination. In the 

 carpus (Fig. 1144) the trapezoid and magnum are united in 

 Bradypus, distinct in Cholcepus: in the former the trapezium is 

 usually fused with the rudimentary first metacarpal. The first 



pr.se 



cor 



FIG. 1141. Shoulder-girdle of Arma- 

 dillo (Dasypus sexcinctus). acr. 

 acromion ; cor. coracoid process ; 

 pr.sc. pre-spinous fossa'; pt. sc. post- 

 spinous fossa ; gp. spine ; gp'. ridge 

 probably marking the anterior 

 limit of origin of the subscapularis 

 muscle. 



tion 



