DISEASES OF MUSCLES. 139 



it as an internal rotator, its point of attachment being outside the 

 axis of rotation of the femur. 



The calf muscles are plantar flexors of the foot, and when 

 weak there is inability to stand on tip-toe. Contracture of the 

 interstitial tissue of the enlarged calf muscles in the pseudo- 

 hypertrophic form of the disease produces talipes equinus. 



The quadriceps is an extensor of the leg. Weakness of this 

 compound muscle causes difficulty in extending the leg to gain 

 the erect position. It also allows the knee to come forwards in 

 advance of the foot in walking. The vastus internus portion 

 when enlarged is easily recognised owing to the increase of 

 the fleshy portion of this muscle which lies just above the inner 

 side of the patella. 



The erector spince muscle of each side is sometimes affected. 

 If at the same time the glutei are intact the resulting lordosis 

 is distinguished from that due to paralysis of the latter muscles 

 by the fact that the pelvis is not tilted forwards. 



OTHER DISEASES AND INJURIES OF MUSCLES. 



A muscle may be said to consist of a mass of contractile tissue, 

 enclosed within a fibrous sheath. As a rule, a muscle has- a 

 free portion or belly between two or more attachments, termed 

 the origin and the insertion of the muscle. The anatomical 

 disposition of certain muscles renders them peculiarly liable to 

 disease or injury. 



Inflammation of Muscle (Myositis). This is usually of a 

 chronic nature, and especially due to tubercle or syphilis. The 

 disease may be primary, or, more usually, in the case of tubercle, 

 secondary. 



Muscles surrounding joints, the seat of tuberculous mischief, 

 are very apt to become involved in the infection, and subsequently 

 the spread of the purulent material is greatly influenced by the 

 sheath of the particular muscle it has invaded, or by the inter- 

 muscular planes it reaches. This influence is particularly well 

 seen in the case of the psoas magnus muscle. This muscle is 



