3U HUMAN EMBRYOLOGY AND MORPHOLOGY. 



by the mesoblastic tissue remaining fibrous, while that which 

 forms the bases of the bones undergoes chondrification. The 

 mesoblastic tissue thus left between the cartilages opens out and 

 forms a synovial cavity and a fibrous capsule. Hence the peri- 

 osteum of the bones is continuous with and derived from the same 

 primitive layer as the joint capsules. The inter-articular 

 cartilages of the knee, for instance, may be simply masses of 

 mesoblast left between the bones, originally part of the condensed 

 mesoblastic bar out of which the femur, tibia and fibula were 

 developed. The inter-articular cartilage of the temporo-maxillary 

 joint may be a derivative of Meckel's cartilage ; that of the 

 sterno-clavicular of the pre-coracoid. The triangular fibro- 

 cartilage of the wrist joint is derived from the ulno-carpal 

 ligaments, and interosseous membrane (Parsons). The cartilage 

 may also contain a post-minimal element (Corner). The cartilages 

 of the knee are of obscure derivation ; they may be parts of 

 muscles formerly inserted on the upper end of the tibia (Sutton). 

 Parsons has shown that in all primates, except man, the 

 external semilunar cartilage is circular in form and is attached 

 to the posterior crucial ligament. 



round lig, 



artic. surface 

 reflected lig. 

 capsule 



Fig. 251.— Showing the Origin of the Ligamentum Teres and Reflected Bundle of 

 the Capsular Ligament. 



The Ligamentum Teres is to be regarded as a part of the capsule 

 of the hip joint which has been cut off by the outgrowth of the 

 articular surface of the head of the femur (Fig. 251). The 

 crucial ligaments are semi-isolated fasiculi from the capsule of 

 the knee joint, separated in a similar manner to the ligamentum 

 teres by the outgrowth of the condyles of the femur (Fig 252). 

 At first the ligamentum mucosum, crucial ligaments and posterior 



