OSTEOLOGY 135 



The length of the xiphoid process is individually variable, 

 and it seems to be least robust in Neotoma. It extends 

 caudad from its articulation with the fourth sternebra, and 

 upon its caudal border is attached the thin, disk-like, 

 xiphoid cartilage, usually largest in Teonoma. The muscles 

 chiefly concerned with the xiphoid process are the pectoralis 

 profundus and the sternocostales. 



Ribs 



There are thirteen pairs of ribs attached to the costal facets 

 of their respective thoracic vertebrae, and they are con- 

 siderably flattened upon the cranial and caudal surfaces. 

 They increase in length to the ninth, after which this meas- 

 urement decreases. Cartilages extend from the sternal ends, 

 and the first seven of these are in turn attached to the 

 sternum. The cartilage of each of the others successively 

 caudad is attached to the cartilage of the rib next craniad, 

 except the thirteenth, and probably occasionally the twelfth, 

 which is free. The thoracic capacity, or space inclosed by 

 the ribs, is relatively somewhat greater in Teonoma. 



extremities 

 Pectoral girdle 



The true affinity of the pectoral and pelvic girdles is usu- 

 ally considered as being with the vertebral column rather 

 than with the ribs. The girdles are so intimately concerned 

 with most of the myological functions of the limbs, however, 

 that for convenience they will be discussed with the respec- 

 tive appendages articulate with them. 



Clavicle. The clavicle is attached by connective tissue 

 to the dorsal border of the lateral process of the manubrium, 

 and by its opposite end to the acromion of the scapula. It 

 is curved in two planes and flattened upon its scapular 

 end. In the specimens at hand it forms the following pro- 



