THE INFRASPINATUS MUSCLE. 



215 



Fig. 231. SUPERFICIAL MUSCLES OF THE 



SHOULDER AND UPPER LIMB, FROM BEFORE. 



(Allen Thomson.) 



1, pectoralis major, its sterno-costal portion ; 

 1', its clavicular portion ; 2, deltoid, its clavi- 

 cular part ; 2', its acromial part ; 3, biceps 

 braclui ; 3', its tendon of insertion ; 3", its 

 aponeurotic slip ; 4, brachialis anticus ; 4', its 

 inner and lower portion ; 5, long head of the 

 triceps ; 5' inner head of the same, seen arising 

 from behind the intermuscular septum. The 

 explanation of the remaining references will be 

 found in the description of fig. 235. 



muscle, and is inserted into the upper 

 of the three facets on the great tube- 

 rosity of the humerus. 



The infraspinatus muscle is of a 

 triangular form, and occupies the greater 

 part of the infraspinous fossa. It arises 

 from the fascia covering it, from the 

 under surface of the spine, and from 

 the inner two-thirds of the dorsal sur- 

 face of the scapula in the fossa, except 

 those parts at the lower angle and along 

 the axillary border, to which the teres 

 muscles are attached. The fibres con- 

 verge to a tendon which, concealed at 

 first within the substance of the mus- 

 cle, is inserted into the middle facet of 

 the great tuberosity of the humerus. 



Relations. The supraspinatus muscle 

 is covered by the trapezius and the acro- 

 mion process. The suprascapular nerve and 

 vessels pass beneath it. 



The infraspinatus muscle is bound down 

 by the aponeurosis which superiorly and 

 externally divides so as to enclose the deltoid 

 muscle. It is covered by the deltoid at its 

 upper and outer part, by the trapezius at its 

 upper and inner part, and by the latissimus 

 dorsi at its lower angle ; in the inter- 

 mediate portion it remains superficial. A 

 small bursa is sometimes present between 

 the tendon and the capsule of the shoulder- 

 joint. 



Varieties. The supraspinatus is very 

 constant in its form and attachments. A 

 slip has been seen passing from its tendon 

 to the tendon of the pectoralis major and 

 the pectoral ridge of the humerus. The 

 infraspinatus muscle is sometimes insepar- 

 ably united with the teres minor. 



The teres minor muscle is placed 

 along the lower border of the infra- 

 spinatus, and is intimately connected 



with that muscle. It arises from a narrow obliquely grooved surface on the 

 dorsum of the scapula close to the axillary border, and from aponeurotic septa 



