Tlie Plathander " (Xenopus laevis). 
347 
quadrate (Q in Figs.) lies near the otic capsule on each side and helps 
to build up the auditory organ ; it sends out processes which sur- 
round a cavity — the tympanic cavity — which is closed to the outside by 
a membrane — the tympanum (T in Figs. 2, 3). The columella, which is 
phylogenetically the hyomandibular bone and functionally a sound-wave 
conductor, abuts with one end on the tympanum whilst the other end it 
is fitted to the fenestra ovalis of the otic capsule. 
Upper Jaiv. — The primitive upper jaw is represented by the palato- 
quadrate cartilage (PQ in Fig. 2). In the Plathander, the palatal portion 
of the cartilage is complete, reaching to the ethmoid ; also the quadrate 
portion is complete. The upper jaw is edged by the membrane bones, 
premaxilla and maxilla (PM and M in Fig. 3), and is articulated with 
the cranium through the pterygoid and the squamosal, both of which are 
developed as membrane bones on the quadrate, the former of the two 
ventral, the latter dorsal. The palato- quadrate cartilage branches into 
two, posteriorly ; the lower branch meets the pterygoid to form the edge 
of the upper jaw while the dorsal branch meets the squamosal to form 
the temporal ridge. Teeth are borne on the premaxillae and on the 
maxillae. 
Lower Jaiu. — The lower jaw articulates with the quadrate, and each 
half of it consists of a dentary (D), an angular (A), and an articular (Ar). 
The angular and the articular are fused ; the dentary is free. The lower 
jaw bears no teeth. 
The Blood-vessels. 
Arterial System (Fig. 4). — Gadow says : " The skin of the back and 
belly is supplied by two great branches of the arteria anonyma, one 
arising proximally, the other distally from the subclavian ; herewith is 
correlated the almost complete absence of the arteria cutanea magna, 
which, as a branch of the pulmo-cutaneous, plays such a prominent role 
in the other Anura. Only in Pipa, but not in Xenopus, is the great 
cutaneous vein represented by a very small branch." 
The word " vein " in the last sentence is obviously a typographical 
error, and should be artery, since this last sentence merely amplifies the 
preceding statement and since the cutaneous vein is very strong in 
Xenopus. 
I find that the skin is supplied with blood by two large vessels, one 
from the subclavian and one from the sciatic, and also by numerous small 
ones from the brachial and the femoral ; that the cutaneous branch of the 
pulmo-cutaneous is still present in Xenopus but that it is small (as 
reported for Pipa) and that it is given otf from the pulmonary artery after 
the latter has entered the lung. 
The carotid trunk, on each side, gives off (1) an artery (L) repre- 
