ETIOLOGY AND OCCURRENCE 31 



between tlie maternal pelvis and some dense part of the fetus. 

 This results in paralysis of the adductors of the thigh if suffi- 

 cient injury is done. 



It is said that nerves become over-stretched and held tense, in 

 certain positions in which animals are obliged to remain while 

 cast in confinement such as in some instances where unusual 

 methods of restraint are employed. When the fore feet are 

 drawn backward in such numner that great strain is put upon 

 the radial nerve, it suffers more or less injury, and this is fol- 

 lowed by partial or complete paralysis which may be temporary 

 or permanent. 



Degenerative changes affecting nerves, as in other tissues, oc- 

 cur and more or less locomotory impediment will follow — this 

 depending upon the nerve or nerves affected and the nature of 

 such involvement. Tumors may surround nerves and eventually 

 the nerve so exposed becomes implicated in the destructive 

 process. Before degenerative changes take place in the nerve 

 substance, in such cases, pressure may completely paralyze a 

 nerve when it is so situated. Melanotic tumors in the para- 

 proctal tissue in some cases, because of the large size of the new- 

 growths, cause paralysis of the sciatic nerve. The author has seen 

 one case of brachial paralysis occasioned by an enormous de- 

 veloiunent of fibrous tissue involving the structures about the 



ulna. 



AFFECTIONS OF BLOOD VESSELS. 



Lameness caused by disturbances of circulation may be due to 

 structural affection of vessels, or functional disorders of the 

 heart, and in some instances, a combination of these causes may 

 be active. 



Direct involvement of vessels is the commoner form of circu- 

 latory disturbance which occasions lameness, and the most fre- 

 quent cause is of parasitic origin. Sclerostomiasis with attendant 

 arteritis, thrombus formation and su])sequent lodgement of em- 

 boli in the iliac, femoral, or other arteries, causes sufficient ob- 

 struction to prevent free circulation of blood, and the character- 

 istic lameness of thrombosis results. 



Indirect injury to vessels may occur because of contused 

 wounds and subsequent inflammation of tissues supplied by such 



