LUXATION OF THE PATELLA 103 



through the perforations to which reference has already been made. 

 These are the vessels which supply the stifle joint. 



Nerve Supply 



The Internal Popliteal Nerve. — This is the direct continuation of the 

 great sciatic nerve. It passes between the two heads of the gastroc- 

 nemius muscle in company with the popliteal artery, but unlike this 

 artery it does not pass along the deep face of the popliteus muscle. It 

 follows the border of the perforatus across the superficial face of the 

 popliteus, and at the inferior border of the latter muscle it is continued 

 as the posterior tibial nerve. This nerve supplies all the muscles at the 

 back of the joint, namely the gastrocnemius, perforatus, and popliteus. 



The External Popliteal Nerve. — A branch of the peroneal-cutaneous 

 division of this nerve passes forwards subcutaneously and ramifies on the 

 external lateral aspect of the joint. 



The Internal Saphena Nerve. — A large branch is given off from this 

 nerve about two inches above the stifle. It passes obliquely downwards 

 and forwards, and splits up into four or five divisions which are dis- 

 tributed subcutaneously on the inner lateral aspect of the joint. 



DISEASES OF THE STIFLE 



LUXATION OF THE PATELLA 



The inner lip of the trochlea terminates at its upper extremity in 

 a blunt ovoid protuberance which stands out in striking contrast to 

 the appearance of the upper extremity of the outer lip. As the 

 patella is pulled upwards by the quadriceps muscles during the 

 process of extension of the stifle, it sometimes happens that the 

 degree of extension is excessive and the patella is drawn upwards over 



