PELVIC GIRDLE. 79 



flexion and extension. The posterior ligament of the 1st 

 interphalangeal joint is of great power to withstand the 

 tendency to overex tension due to the weight of the body : 

 it is united laterally to the tendon of the flexor sublimis and 

 extends up the posterior surface of the 1st phalanx to become 

 confounded with the sesamoid ligaments of the metacarpo- 

 phalangeal joint. 0. C. 279. 



PELVIC GIRDLE. 



B. 151. A section of the sacrum and pelvic girdle of a Man. 

 The dorsal portion of the sacro-iliac articulation is firmly 

 united by fibrous tissue, the ventral shows a distinct 

 synovia! cavity. 



HIP. 



B. 152. The os innominatum and femur of a large Tortoise 

 (Testudo indica). 



The hip-joint is laid open to show that the ligamentum 

 teres is absent. This simple form of joint obtains at the hip 

 in all Chelonian reptiles. 0. C. 255 A. 



Presented ly W. Clift, Es<j. 



B. 153. The right os innominatum, os marsupiale, and femur of 

 a Duck-billed Platypus (Ornithorhynchue anatinns). 



The anterior part of the capsule of the hip-joint has been 

 removed to expose the head of the thigh-bone, and the 

 cotyloid cavity, and to show that the ligamentum teres is 

 absent in this species. 



B. 154. The left os innominatum, os marsupiale, and femur of 

 Echidna aculeata. 



The head of the femur is turned out of the cotyloid 

 cavity, to show the absence of the ligamentum teres. There 

 is a foramen at the back part of the cotyloid cavity, which 

 is deficient at that part, as it is in birds. 0. C. 255 D. 



B. 155. Left hip-joint of a Koala (Phascolarctus cinereun] . 



The joint has been opened to show the ligamentum teres, 



