1901.] AlfATOMY OP CHETSOCHLOEIS TREVELTANI. 33 



away from the rudimentary coracoid, and all ligamentous con- 

 nections between the two are obliterated. 



To the comparative anatomist the contrast between the arrange- 

 ment met with in this animal and the Three-toed Sloth {Bradypus) 

 is very striking. In the latter animal the coraco-clavicular ligament 

 forms the only union between the clavicle and the scapula, while 

 in the Golden Mole it is absent altogether. The Armadillo, as 

 will be seen on referring %o my paper \ forms a transition between 

 the two. 



The acromio-clavicular articulation is very interesting. A small 

 bone is interposed between the acromial end of the clavicle and 

 the acromion, and there is a synovial cavity on each side of it ; 

 this is the only instance I have hitherto noticed of the presence 

 of such a bone, and the possibility of its being homologous with 

 the interarticular meniscus of the same joint in man at once occurs 

 to the mind. Personally, I should be more inclined to regard the 

 two structures as analogous than homologous, because intraarticular 

 menisci are so often found where rotation is combined with hinge 

 or gliding movements ; and in ChrysocMoris, partly owing to the 

 absence of the coraco-clavicular ligaments, the rotation or pendulum 

 movement of the scapula is very free in addition to gliding move- 

 ment. Probably this little bone is an ossified meniscus developed 

 to meet the requirements of the joint. Of course this is merely a 

 surmise, but it seems borne out by the facts at my disposal. 



The great differences in the detail of the bones and joints 

 connecting the shoulder-girdle with the trunk in the Mole (Talpa) 

 and the Golden Mole are very obvious. 



The shoulder-joint differs little from that of a generalized 

 mammal, it is chiefly remarkable for the lateral compression of the 

 head of the humerus. The oblique middle gleno-humeral ligament 

 is well marked, but does not project at all into the cavity of the 

 joint ; it has the typical mammalian attachments. It becomes 

 tight in extension and external rotation. 



The elbow is chiefly remarkable for the enormous development 

 of the olecranon, but there is no upward extension of the back of 

 the head of the radius as in the Mole. During flexion of the 

 joint considerable lateral movement is allowed, as well as rotation 

 of the radius and ulna together, through an axis passing between 

 the two bones and parallel to their long axes ; this movement is 

 possible to the extent of about | of a circle, and is quite distinct 

 from pronation of the radius, which is only possible for about ^ of 

 a circle. As there is so little true pronation one would not expect 

 an orbicular ligament, nor can anything of the kind be found. 

 The external lateral ligament runs to the outer side of the head of 

 the radius, M bile the internal is fan-shaped and passes down to 

 the inner margin of the sigmoid cavity of the ulna. 



The wrist-joint resembles that of most mammals in which there 

 is little pronation and supination of the forearm. There is no 



^ Op. cit. p. 50. 

 Peoc. Zool. Soc— 1901, Vol. I. No. III. 3 



