J. Playfair MceMurrich . 185 
tions of the palmaris communis shown in Fig. 2. They have, however; 
undergone a very important modification by the extension of their origin 
proximally upon the bones of the forearm, so that they have acquired 
a more longitudinal direction, a condition which is associated with a 
reduction of the width of the volar cartilage into which they are inserted 
as compared with the amphibian palmar aponeurosis. The proximal 
extension has occurred chiefly in connection with portion II of the 
muscle and with it there has been a certain amount of extension of its 
origin radialwards. The palmaris profundus I has retained its original 
oblique direction and also its primary origin from the lower end of the 
ulna and the ulnar carpal bones, and has thereby been brought into 
somewhat different relations to the other portions of the profundus than 
obtained in the amphibia. In a section through the distal part of the 
forearm of Amblystoma the profundus I appears as the most radial of 
the profundus muscles, while in the reptilia it seems to be the most ulnar. 
The identification of the muscle in the two groups rests mainly on its 
nerve supply and, if this be accepted as a sufficient criterion, an explana- 
tion is to be sought for the apparent difference in its position. I believe 
that this can be found in the change in the direction of the second and 
third portions of the profundus and the migration of their origins 
proximally, the profundus I being thereby permitted to occupy exclu- 
sively the lower part of the ulna and the ulnar side of the carpus, and 
since its insertion in the reptilia is into the dorsal surface of the volar 
cartilage, while the other portions of the profundus insert into its proxi- 
mal border, there is no obstacle in the way of a conversion of the ar- 
rangement seen in the amphibia into what occurs in the reptilia. 
One muscle of the amphibian forearm I have not been able to recog- 
nize in the reptilia. This is the ulno-carpalis. The ramus ulnaris of 
the superficial branch of the inferior brachial nerve passes across the 
ventral surface of this muscle and descends the arm upon its ulnar 
surface and in the reptilia the corresponding nerve has the same rela- 
tions to the second part of the palmaris profundus, using that desig- 
nation for the portion of the palmaris communis which has been identi- 
fied with the amphibian profundus II. Arguing from this topographic 
relation, it seems possible that the muscle has been incorporated 
in the reptilian profundus IT. Such a condition would, however, neces- 
sitate a decided alteration of the insertion of the ulno-carpalis, which 
must have shifted from the carpus to the palmar aponeurosis and, 
furthermore, I find no branches of the ramus ulnaris, which supplies 
the amphibian muscle, entering the substance of the reptilian palmaris 
profundus. While I hesitate to express a conviction that the muscle 
