THE SHOULDER JOINT 



409 



Anteriorly, the Coraco Humeralis, and Flexor Brachii. 



Externally, the Antea Spinatus, and Postea Spinatus. 



Posteriorly, the Scapulo-Humeralis Posticus, etc. 



Internally, the Subscapularis, etc. 



Whenever, therefore, any violent strain is thrown upon the joint, which 

 would force the head of the humerus forwards, the Coraco Humeralis and 

 Flexor Brachii contract and prevent the accident. 

 In the same manner, each of the above muscles acts 

 in its own direction, and the result is that dislocation 

 of the humei-us in the horse is extremely rare. 



The movements of the shoulder joint in the 

 horse are much more limited than in man, and indeed 

 they are almost confined to flexion and extension. 

 When all the muscles are cut away from the joint, 

 rotation and circumduction may be easily effected ; but 

 in examining its movements during life, it will be 

 evident that neither one nor the other of these acts 

 can be effected in any appreciable degree ; this is at 

 ■once proved if it is attempted to tui'n the foot in- 

 wards or outwards, when it is flexed at the knee, 

 during the life of the horse, for beyond the slight 

 motion of the whole limb, including the scapula, the 

 foot is firmly fixed, and there is not the slightest 

 rotation or circumduction at the shoulder joint. With- 

 out the power of pronation and supination possessed 

 by man, and partially by the dog and cat, the above 

 actions would be worse than useless, and it is alto- 

 gether a mistake to ascribe to any other of the domestic 

 animals, as Chauveau has done, in addition to flexion 

 and extension of the shoulder joint, the four move- 

 ments of abduction, adduction, circumduction, and 

 rotation.-"- It would much puzzle that generally accu- 

 rate anatomist to turn the horse's foot up in front so 

 that its possessor could see the sole ; yet if circum- 

 duction and adduction were permitted, this could 

 readily be done as by the domestic cat or dog in 

 licking the inside of the fore-^ The shoulder 



joint is, in fact, a true hinge (ginglymus) in the horse, ass, cow, sheep, 

 and goat, but in the first of these animals it is more especially limited 

 in its movements, by the enormously powerful muscles which surround 

 the joint, and which are constantly tense, though extremely elastic, and 

 giving way to every voluntary movement. It is a beautiful provision of 

 nature, to enable the horse to bear the shocks which his shoulders have 

 to sustain in coming down from a leap with a great weight on his back, 

 and without it he would be rendered comparatively useless to man. 



Fio. 45. — Profile View of 



THE ScAPULO-HuMERAL, 



OR Shoulder Joist. 



A. Inferior third of sca- 



pula. 



B. Coracoid process of 



scajjula. 



C. Analogue of the acro- 



mion process. 



T>. Rim of glenoid cavity. 



E. Superior third of hu- 

 merus. 



1. Capsular ligament. 



2. Tendon of the coraco- 



radialis muscle. 



^ Under certain circumstances, lame and otherwise injured horses prove the possession- 

 of those movements claimed by Chauveau, but only to a very limited extent. — Editor. 



