CHAPTER V 



THE JOINTS 



THE SHOULDER JOINT 



The shoulder joint is formed between the articular head of the humerus 

 and the glenoid cavity ot the scapula. The former is a large hemispheri- 

 cal piece of bone situate at the back ot the upper extremity of the 

 humerus. It is entirely articular, and presents a similar degree of slight 

 convexity in all directions. It is surrounded by a faintly-defined 

 roughened edge which gives attachment to the capsular ligament. In 

 front of the articular head is a transversely elongated, depressed area of 

 bone which presents numerous perforations for the passage of blood- 

 vessels and nerves into the cancellated tissue. This area is about an inch 

 in breadth, and in the depression in the living animal there is usually 

 present a considerable quantity of adipose tissue. In front of this depres- 

 sion again is the bicipital groove. This, in the horse, is divided into 

 two parts by a prominent median ridge, the two parts of the groove and 

 the ridge separating them being smooth for the play over them of the 

 tendon of the biceps muscle. The median ridge is about half an 

 inch in height, and, taking into consideration also the thickness of muscle 

 and skin, the distance from the cutaneous surface on the anterior aspect 

 of the joint to the anterior border of the articular head of the humerus is 

 about three to three and a half inches. 



The glenoid cavity is an articular area for the accommodation of the 

 head of the humerus. Its degree of concavity therefore corresponds to 



