213 MUSCLES OF THE UPPER LIMB. 



The extensor ininimi digiti is a slender muscle which is placcrl 

 between the extensor communis digitorum and the extensor carpi 

 ulnaris, and arises by means of a thin tendon in common with the ex- 

 tensor communis. The tendon in which it ends occupies a groove 

 between the radius and ulna, passing through a special compartment 

 in the annular ligament, and joins the fourth digital tendon of the 

 common extensor. 



Vcu'icth's.—Tlii^ muscle, like that preceding, and the same occurs in the indi- 

 cator muscle afterwards described, is subject to an increase in the number of its 

 tendons of insertion, and in a large proportion of the cases the additional 

 tendon is inserted into the ring-finger. The entire absence of the muscle has 

 also been observed. In the case of the indicator, the additional tendon is most 

 frequently inserted into the middle finger, constituting the extensor medii, which 

 is sometimes separate in the whole length of the muscle. 



The extensor carpi ulnaris, the most internal of the muscies 

 descending on the back of the forearm, arises from the external con- 

 dylar eminence of the humerus by the common tendon and prolongation 

 of that structure ; from the posterior border of the ulna, below the 

 anconeus, for about the middle third ; and from the fascia of the fore- 

 arm. The muscular fibres derived from these sources incline somewhat 

 inwards, and end in a tendon, which runs through a special groove in 

 the carpal end of the ulna and a separate sheath in the annular ligament, 

 and is inserted into the base of the metacarpal bone of the little finger 

 on its posterior aspect. 



Vin'ictics. — This muscle is frequently connected with the short abductor minimi 

 digiti. It also sometimes sends a prolongation to the extensor tendons on the 

 back of the little linger, which has been named ulnaris quinti. 



The DEEr-SEATED MUSCLES ou the back of the forearm are five in 

 number, the supinator brevis, the three extensors of the thumb, and the 

 extensor of the index-finger. 



The supinator radii brevis muscle arises from the external lateral 

 ligament of the elbow-joint, and from the annular ligament of the radius ; 

 also from a rough depression below the sigmoid cavity of the ulna, and 

 from the outer border of that bone for two inches. The fibres of the 

 muscle, derived from these points of attachment, as well as from a 

 tendinous expansion on the surface, pass obliquely round the upper 

 part of the radius, covering it closely except at the inner side, and are 

 inserted into that bone for rather more than a third of its length, 

 passing down to the upper margin of the insertioli of the pronator 

 teres. It is pierced by the posterior interosseous nerve. 



Varieties. — This muscle is subject to more or less division at the place of 

 passage of the posterior interosseous nerve, and occasionally the insertion of an 

 accessory slip takes place into the biceps tendon or tuberosity of the radius. A 

 set of short fibres passing round the upper part of the radius has received the 

 name of tensor ligamenti orbicularis anterior (W. Griiber, Cruveilliier). 



The extensor ossis nietacarpi pollicis muscle (abductor longus 

 pollicis, — Alb.) arises from an elongated depression on the radial side 

 of the posterior surface of the ulna below the origin of the supinator 

 brevis, from a similar extent of surface of the radius below the insertion 

 of the same muscle, and from the interosseous membrane between. 

 Thence descending obliquely outwards, it ends in a tendon, which 

 passes, in company with the extensor primi internodii pollicis, through 



