574 



SHOULDER JOINT (NORMAL ANATOMY). 



than at the circumference ; whilst the reverse 

 is true of the glenoid cavity, the cartilage 

 being there of greater depth at the circum- 

 ference than at the centre. 



The anatomical disposition of(c.) the synovial 

 membrane, can be more conveniently studied 

 after the ligaments have been examined. 



3. Connecting Media. Capsular ligament. 

 This is a fibrous expansion which in its general 

 character resembles the capsular ligament of 

 other articulations. The capsule of the shoulder 

 joint is remarkable for its capaciousness, and 

 consequent laxity an arrangement which per- 

 mits the great freedom of motion enjoyed by 

 this articulation. It embraces the margin of 

 the glenoid cavity above, and is prolonged upon 

 the tuberosities of the humerus interiorly ; 

 hence it may be described as a sac having two 

 apertures, of which the lower is by far the 

 larger. Viewed externally, its form is that of 

 a hollow cone, the base of which is placed 

 inferiorly. The fibres which compose the 

 capsule are extremely irregular in direction, 

 nor are they of uniform strength or thickness. 

 The capsule is very thin, posteriorly and also 

 internally ; in the latter direction, it is almost 

 aways deficient, so that the cavity of the joint 

 is continuous with that of the synovial bursa, 

 beneath the tendon of the subscapularis 

 muscle ; more rarely, an opening in the cap- 

 sule establishes a communication between the 

 serous cavity of the shoulder joint and a 

 bursa under the infra-spinatus muscle. The 

 capsule possesses considerable strength an- 

 teriorly and above, being there reinforced by 

 a thick bundle of fibres, sometimes described 

 as a distinct ligament, under the name of 

 coraco-humeral, or accessory. These fibres 

 are attached superiorly to the under surface 

 of the coracoid process, they thence follow an 

 oblique course downwards and outwards, be- 

 come incorporated with the proper fibres of 

 the capsule, and are traceable inferiorly to the 

 great tuberosity of the humerus, crossing an- 

 terior to its bicipital groove. Inferiorly, or 

 towards the region of the axilla, the capsule 

 possesses much intrinsic strength, though here 

 totally devoid of any muscular or tendinous 

 coverings. When the arm is much abducted, 

 the head of the humerus presses strongly 

 against this part of the ligament, which some- 

 times gives way, and the head of the bone 

 escaping from the glenoid cavity, between the 

 subscapular muscle, and the long head of the 

 triceps, dislocation into the axilla is produced. 

 In this accident, the head of the humerus 

 generally detaches the subscapular muscle 

 from the bone, and lies between that muscle 

 and the subscapular fossa. The anatomist 

 will not fail to observe that the subscapular 

 nerve, as it runs from the brachial plexus 

 outwards, to wind round the neck of the 

 humerus, is closely related to this portion 

 of the capsule which may be seen from 

 the axilla, between the triceps and subsca- 

 pularis muscles ; and can, therefore, easily 

 understand why the nerve in question should 

 be sometimes torn or compressed, when the 

 head of the humerus has been dislocated 



downwards and inwards ; this complication 

 of the axillary dislocation gives rise to para- 

 lysis of the deltoid muscle, partial or com- 

 plete, temporary or permanent, according to 

 the degree of injury which the nerve may 

 have sustained. 



The exterior of the capsular ligament is in 

 close relation superiorly with the supra-spinatus, 

 and posteriorly with the infra-spinatus and 

 teres minor muscles ; inferiorly, it is con- 

 nected with the scapular origin (long head) of 

 the triceps; whilst anteriorly, it is covered and 

 partly replaced by the subscapularis. With 

 the intervention of the capsular muscles, it is 

 also related on its external, anterior, and 

 posterior aspects to the deltoid muscle, and 

 above to the coraco-acromial triangle. A 

 large bursa is situated beneath the deltoid, 

 and separates this muscle from the exterior 

 of the capsule ; it also gives an extensive in- 

 vestment to the tendons of the capsular 

 muscles, and is evidently designed to favour the 

 very free motit-ns which those parts enjoy. 



The long tendon of the biceps, placed ex- 

 actly upon the anterior aspect of the bone, 

 escapes from beneath the lower edge of the 

 capsule, which here arches across the bicipital 

 groove, and converts it into a canal ; the 

 capsule is not therefore perforated by the 

 tendon of the biceps, as is stated by many 

 anatomists. A portion of the synovial mem- 

 brane descends with the tendon below the 

 edge of the capsule, is again reflected on the 

 groove, and so re-ascends into the joint, having 

 formed a small " cul-de-sac," without the ar- 

 ticulation. 



From these relations with the surrounding 

 muscles, the capsule derives much of its 

 strength : the tendons of the four capsular 

 muscles are inseparably united to the fibres of 

 the ligament, which are prolonged inferiorly, 

 as far as the lowest portion of the humeral 

 tuberosities; posteriorly, it derives some fibres 

 from the triceps ; and from the upper edge of 

 the tendon of the great pectoral muscle, (at 

 its insertion into the anterior lip of the bi- 

 cipital groove,) a fibrous fasciculus ascends, 

 and likewise becomes identified with the cap- 

 sule ; this prolongation has been described, 

 under the name of " suspensory fraenum," by 

 Winslow. 



It must be obvious from this description, 

 that the capsular ligament alone cannot 

 maintain the bones of the shoulder joint in 

 opposition: from its great laxity, it permits a 

 considerable separation of the osseous sur- 

 faces, and they are maintained in contact with 

 each other mainly by the tonic contraction of 

 the surrounding muscles (which are placed in 

 the most favourable position to accomplish 

 this important object). Accordingly, in para- 

 lysis of the upper extremity, the limb be- 

 coming elongated, one or two fingers can be 

 pressed into the joint towards the glenoid 

 cavity, now abandoned by the head of the 

 humerus ; and, owing probably to a some- 

 what similar condition of parts, spontaneous 

 dislocation of the humerus has been known 

 to occur in the debilitated state of the sys- 



