232 THE MUSCLES OF THE UPPER LIMB. 



to one or two of them. More frequently, however, the increase in number of the tendons 

 is limited to the index or middle finger alone. An additional slip to the thumb is occasionally 



The extensor minimi digiti is a slender muscle which arises from the fascia 

 of the forearm, and from the intermuscular septa separating it from the extensor 

 communis digitorum and the extensor carpi ulnaris. The tendon in which it ends 

 occupies a groove between the radius and ulna, passing through a special compart- 

 ment in the annular ligament ; on the back of the hand it becomes split into two, 

 the outer division being joined by a slip from the fourth tendon of the common 

 extensor, and both parts end in the dorsal expansion of the little finger, in the 

 formation of which this muscle takes by far the greater share. 



Varieties. An origin from the external condyle of the humerus by means of a thin 

 fibrous slip forming part of the common tendon is occasionally present (5 per cent.). The 

 tendon of insertion is sometimes undivided (10 per cent.), or gives a slip to the ring 1 finger 

 ((> per cent.). Absence of the muscle is rare, but fusion of the belly with the extensor 

 communis digitorum is not uncommon (4 per cent.). (Gruber, " Beobachtungen," Heft iii, 

 1882, and Virchow's Archiv, xcix, 1885.) 



The extensor carpi ulnaris, the most internal of the muscles descending on 

 the back of the forearm, arises from the external condyle of the humerus by the 

 common tendon, from a strong intermuscular septum on its outer side, and from the 

 fascia of the forearm. The belly of the muscle is in its middle third closely bound 

 down to the posterior border of the ulna by the fascia, and it occasionally receives a 

 few additional fibres from this portion of the bone. The fleshy fibres are collected 

 round a tendon which becomes free a little above the wrist, and runs through a 

 special groove in the carpal end of the ulna and a separate sheath in the annular 

 ligament, to be inserted into the tuberosity on the base of the fifth metacarpal bone. 

 There is sometimes a small bursa beneath the tendon of origin. 



Varieties. The extensor carpi ulnaris has been seen 1, double throughout, 2, reduced 

 to a tendinous band, and 3, inserted partially into the fourth metacarpal bone. In very 

 many cases (62 per cent.) a slip is continued from the insertion of the tendon anteriorly, over 

 the opponens minimi digiti, to be inserted into the fascia covering that muscle, the 

 metacarpal bone, the capsule of the metacarpo-phalangeal articulation, or the first phalanx of 

 the little finger. The slip is sometimes joined or replaced by a muscular fasciculus arising 

 from or in the neighbourhood of the pisiform bone. (Gruber, " Beobachtungen," Heft ix r 

 1889). 



The ulnaris quinti digiti is a muscle that has been met with once by W. Gruber, arising from 

 the posterior surface of the ulna in its lower half, and inserted into the base of the first phalanx 

 of the little finger. It is occasionally represented by a fasciculus from the belly of the 

 extensor carpi ulnaris, very frequently (44 per cent.) by a dorsal slip from the tendon of that 

 muscle, which may be inserted into either the metacarpal bone or the first phalanx, or may 

 join the extensor tendon of the little finger. (Gruber, "Beobachtungen," Heft v, 1884.) 



The DBEP-SEATED MUSCLES on 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, from the annular ligament of the radius, and from the supinator 

 ridge and the hinder part of the bicipital hollow of the ulna, extending downwards 

 a short distance along the outer border of the bone. The fleshy fibres derived from 

 these points of attachment, as well as from a tendinous expansion on the surface, 

 which can be followed up to the external condyle, 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, reaching down to the insertion 

 of the pronator radii teres, and being limited in front and behind by the anterior 



