10 H. ST. J. BROOKS ON THE 
upwards nearly to the tip of the olecranon (Fig. 6, ex. 1, 2, and 3). The muscle is 
subcutaneous for the upper three-fourths of its extent. The lower part of the 
muscle is placed under cover of the ext. carpi ulnaris and ext. minimi digiti, and is 
continued into a tendon which traverses the same compartment of the annular 
ligament as the tendon of the common extensor. It divides in the hand into three 
tendons, which proceed to the thumb and to the index and middle fingers, and are 
inserted into the deep surface of the corresponding tendons of the common extensor. 
The ext. minimi digiti is a slender muscle, which is deeply placed in the upper part 
of the forearm, and first becomes superficial near the wrist (Mig. 6, ex.m.d.). It 
arises from the external condyle under cover of the ext. carpi ulnaris, and forms a 
small ribbon-like band of muscle, which is compressed between the ext. carpi ulnaris 
and the ext. communis digitorum. In Fig. 5 it is exposed by the reflection of the 
ext. carpi ulnaris, and is seen in its natural position lying against the deeper fibres 
of the ext. communis digitorum. Its tendon accompanies the tendon of the ext. 
carpi ulnaris through the annular ligament, and divides in the hand into two slips. 
One of these blends with the fifth division of the common extensor and with the 
longer of the two portions of the tendon of the ext. carpi ulnaris to the extensor 
tendon of the little finger. The other slip (eat. annularis) crosses under cover of 
the fifth division of the tendon of the common extensor, and joins the ulnar side of 
the fourth or annular division of the same tendon. 
The posterior annular ligament is divided into four compartments, which 
transmit the extensor tendons in the following order, commencing on the radial 
side :—(1) Ext. ossis metacarpi pollicis ; (2) Eat. carpt radiales longior et brevior ; 
(3) Eat. communis digitorum and ext. indicis et pollicis; (4) Hat. minima digite 
and eat. carpi ulnaris. 
The musculo-spiral nerve divides at the elbow-joint into a radial and a posterior 
interoseous branch. The radial passes downwards on the back of the forearm under 
cover of the integument to the dorsum of the hand; here it divides into a number 
of large branches which communicate in a plexiform manner, and end in branches to 
all the digits. The posterior interosseous nerve has essentially the same course and 
relations as in Man. It supplies all the above described muscles, with the exception 
of the anconeus. I could not follow it further than the wrist. The nerve to the 
anconeus escapes through the fibres of the triceps, and passes between the external 
condyle and the olecranon process to end in the anconeus muscle. On account of 
the great development of the external condyle, this nerve is more deeply placed 
than in Man. 
Mecxker has noticed the phalangeal insertion of the eat. carpz ulnaris in the 
Ornithorhynchus, and GruBerR has traced the tendon of the same muscle to the 
ungual phalanx in the Echidna.” 
*I have unfortunately not been able to consult the text of Mxckgn’s Ornithorhyncht paradoxi 
deseriptio anatomica, but 1 have seen one of the plates which accompany this work. I extract the 
