72 



structure of the principal joints of the lower extremity, and on the 

 degrees of mobility of which they are susceptible. 



In the hip-joint the most remarkable circumstance is the freedom 

 of motion in the rotation inwards ; this is, however, more limited 

 than in the opposite direction. The motions of flexion and ex- 

 tension, abduction and adduction, are also very free. On examining 

 the cause of the limitation of the inward rotation, he found it to be 

 a strong band of ligamentous fibres arising from the posterior margin 

 of the cotyloid cavity, and passing along the back part of the cap- 

 sule to the root of the great trochanter ; when this was divided the 

 rotation inwards was as free and extensive as happens in other cases 

 after a division of the ligamentum teres. The synovial membrane is 

 reflected over a greater patt of the anterior and upper than of the 

 back and under part of the cervix femoris. The marginal ligament 

 of the articular cavity is four lines in depth, a remarkable thickness 

 for the size of the cavity. The blood-vessels enter the joint by the 

 usual notch, and supply abundantly the process of synovial and 

 adipose substance called the gland of Havers. 



The motion at the knee-joint is sufficiently free to allow the heel 

 to be brought to the buttock, and even beyond, as in natural 

 flexion it is carried external to the thigh. The only circumstances 

 remarkable in the structure of the joint are, that the internal lateral 

 ligament is longer, and the ligamentum mucosum stronger and of a 

 more ligamentous nature, than in the human subject. 



The motion at the ankle-joint is so free, that the dorsum of the 

 foot can be brought into apposition with the fore-part of the leg ; 

 and it is worthy of remark, that when this motion is produced, the 

 effect on the tendons passing behind the ankle-joint is such, as to 

 cause a flexion of the toes similar to that which is produced in 

 perching birds by bending the tarsus upon the ]eg. In the opposite 

 direction the foot may be brought so far back as to form a right 

 angle with the leg. Lateral motion is also very free, especially the 

 turning of the sole inwards, to which aspect it naturally inclines. 

 A certain degree of motion is allowed between the first and second 

 set of tarsal bones. The ligaments of the ankle-joint are disposed 

 as in the human subject, one at the inner and three at the outer side. 



The ligaments that connect the metatarsal bone of the thumb to 

 the internal cuneiform bone, are two in number, one at the upper 

 and the other at the lower or plantar aspect ; these limit the motions 

 of flexion and extension, but allow very freely abduction and ad- 

 duction. From this circumstance when the peroneus longus acts on 

 the foot in turning the sole outwards, its tendency to bend the me- 

 tatarsal bone upon the foot is resisted, and this bone is rendered a 

 fixed point without the necessity of the counteraction of a mus- 

 cular antagonist. 



