6 CONTENTS OF A BONE CAVE. 



tuberosity. The distal end of the humerus is moderately expanded in the trans- 

 verse direction. The external epicondyle is protuberant; the internal wanting. 

 The condyles have the ulnar and radial portions about equal, and the intertrochlear 

 ridge is represented by an obscure angle. The external or ulnar keel is prominent. 

 On the posterior face a rather short, median, concave, trochlear face represents the 

 two anterior faces. 



Both ulna and radius are rather slender ; at the middle of their length the former 

 is "compressed, and the latter is depressed, both moderately. The olecranon is 

 prominent and subcylindric. The head of the radius is a rather wide oval, directed 

 downward and outward, while the coronoid process of the ulna is directed upward 

 and inward. The fore-foot is unknown. 



Posterior Limb. The section of the neck of the ilium is an equilateral triangle, 

 and is quite long ; the crest is not preserved, but from the form of the sacrum may 

 have had more extent than in many rodents. There is a strong tuberosity in the 

 position of the anterior inferior spine. The fossa ligamenti ten's and the incisura 

 acetaluli are strongly developed, the latter not perforate. The posterior bones of 

 the pelvis are unknown. 



The femur has several marked peculiarities. One of these is the great develop- 

 ment of the great trochanter, which is really an undiminished continuation of the 

 shaft for some distance beyond the head. The head is relatively small, and is more 

 than half a sphere ; its ligamentous pit is distinct and isolated ; the neck is abruptly 

 contracted within the head, and projects at right angles to the shaft. The posterior 

 base of the great trochanter is deeply excavated. The little trochanter is a promi- 

 nent tuberosity. The condyles have a predominating inferior exposure. The 

 patellar groove is wide and not elevated. There is a deep fossa in the external 

 epicondylar region. 



The head of the tibia is expanded laterally, and the upper part of the crest is 

 replaced by a plane surface, as in the corresponding bone in man. The spine is 

 prominent, a portion belonging to each of the articular faces, which are separated by 

 a deep groove. The upper portion of the shaft is deeply grooved on the external 

 face. The distal portion of the shaft is relatively slender. The distal extremity is 

 expanded inwards. The astragalar facets are oblique, the external is larger than 

 the internal, and they are well separated by an obtuse ridge. There are two pro- 

 cesses on the internal border, which are separated by a deep tendinous groove, 

 which is in most of the specimens bridged over by a lamina connecting the pro- 

 cesses. The posterior of the two processes is the most elongate : it corresponds to 

 a process of the astragalus, which extends backwards and inwards from the internal 

 trochlear face. When extension of the foot is attempted, these processes come in 

 contact, and prevent further movement. The amount of extension from the hori- 

 zontal which this arrangement permits, is 45. When at this point the processes 

 constitute a support to the Aveight of the animal in addition to that furnished by 

 the usual astragalar facets. The fibular plane is triangular, and has a posterior as 

 well as exterior exposure. 



The astragalus is quite depressed, and the convexity of its rotular surfaces is not 

 great. The latter are of unequal size, the external having four times the extent of 



