MORPHOLOGY OF THE EXTENSOR MUSCLES. 13 
peroneus longus and brevis, ext. brevis digitorum and ext. longus digitorum. Its ter- 
minal twigs could be followed with some difficulty to the tarsus. A branch from 
the anterior crural nerve (fig. 7, a.cr.) passes through the fibres of the quadriceps 
and crosses in front of the external condyle to end in the two divisions of the 
tibialis anticus muscle.* 
The following points stand out prominently from this description :— 
1. In both fore and hind limbs the three sectors of the superficial stratum 
are now completely separate. 
2. The superficial stratum in the hind limb has not retained any origin 
from the femur. 
3. The deep stratum in the fore limb, and still more remarkably in the 
hind limb, arises from a more proximal point in the limb than in the 
lower forms already considered. 
4. The metacarpal heads of the short extensor are wanting. 
The Extensor Muscles in the Forearm -and Leg of Man. 
A brief account may now be given of the changes which have probably occurred 
by which a condition resembling Hatteria has attained to the condition which is 
present in Man. The history of each muscle will be considered separately in the 
second part of this paper. 
Fore limb.—In the superficial stratum the following changes have taken place : 
—The ulnar sector has retained very much the same connections as in Hatteria. 
The anconeus, however, has become more segmented from the ext. carpi ulnaris, and 
shows a tendency to unite with the triceps. The tendinous slip from the ext. carpi 
ulnaris to the phalanges of the fifth digit is not normally developed, but sometimes 
appears as an ulnaris quinti digiti. Radial sector.—The supinator mass is com- 
pletely segmented into supinator longus and supinator brevis, and the ext. carpi 
radialis has divided into two muscles, longior and brevior ; moreover, the tendons 
of these muscles have wandered towards the ulnar side, and are inserted into the 
second and third metacarpal bones. Intermediate sector.—The ext. longus digitorum 
has no longer any hold on the metacarpal bones, but is inserted exclusively into the 
phalanges of the digits. 
* This nerve is described in the following words by Ruce :—‘“‘ Der Muskelast des Plexus cruralis 
begibt sich auf der Vorderfliche des Oberschenkels vom Stamme des Nervus cruralis am medialen Rande 
des zur Patella verlaufenden Extensor cruris in die Tiefe, durchbohrt die lateralen Oberschenkelmuskeln, 
um im distalwarts gewendeten Verlaufe schliesslich lateral yon der Patella frei tiber den Condylus 
externus femoris und das Kniegelenk, zwischen der Fibula und Tibia, auf den Unterschenkel tiberzugehen. 
Wir finden den Nerven auf Figur 1 u. 2 in der Gegend der Tibiofibularverbindung. Er spaltet sich in 
mehrere Aeste, welche sich im M. tib. ant. sowohl als auch im Ext. hall. long. auflésen.” (op. cit., 
p- 597). I may add to this description that as the nerve passes through the substance of the quadriceps it 
gives off twigs to the muscular substance, reminding us of the manner in which the “nerve to the 
anconeous” gives twigs to the triceps. 
