Mar., 1903.] 
Spelerpes longicaudus. 
3 8 3 
pact and dense cartilaginous tissue, from which all trace of car- 
tilage cells has disappeared. 
Meckel's Cartilage — (Plates 8, 9, me ) Meckel’s Cartil- 
age forms the basis and largest part of the lower jaw. It articu- 
lates in front with the bar of the lower labial, and fuses there, 
more or less completely, with its fellow of the opposite side. 
Behind, it articulates strongly with the quadrate (Plate 8, qd.). 
The cartilages are slender and rounded anteriorly, but become 
much heavier and more ovoid as they near their articulation with 
the quadrate. The coronary process is plainly marked, just in 
front of the posterior articulation, and directly under the optic 
foramen. The massive temporal and masseter muscles, which 
have their attachments on this process, together with the heavy 
pillar of the quadrate, form a bulging prominence which is readily 
discernible with the unaided eye. 
The Quadrate.—* Plate 8, qd.). The quadrate is fused com- 
pletely above with the trabecula, at a point dorsal to the second 
foramen, as before stated. Above and behind it fuses with the 
auditory capsule, while below it sends a heavy vertical bar to 
articulate with Meckel’s cartilage. The quadrate is the heaviest 
solid cartilage in the skull at this period, and helps to form the 
rim of a deep protective socket within which the eyeball rests. 
The fusion of the quadrate with the capsule of the ear is only slight 
at this stage, but the mesoderm between the two parts is seen to 
be rapidly chondrifying, and indicates an extensive fusion later. 
Auditory Capsule. — The auditory capsule, although not com- 
pletely ehondrified, can be traced very readily. The two capsules 
form the side wall of the skull, and indications of their juncture 
over the top of the brain cau be detected. They are fused with 
the quadrates in front and with the trabeculae cranii below, but 
their posterior extremity is a free rounded surface. At the 12 
mm. stage, th.refore, the brain lies exposed above, but is pro- 
tected laterally by the heavy auditory capsules and ventrally by 
the broad trabecular plate, and by the parachordals. The semi- 
circular canals in the ear are fully formed, and there is full nerv- 
ous connection with the brain. The circular (fibrous; patch so 
prominent in the frog at a similar stage can be detected, but with 
difficulty. It is the foreshadowing of the future stapes. 
Teeth. — Teeth appear on the upper and lower labials and on 
both the trabeculae cranii and Meckel’s cartilage. They are well 
along in development, and can be seen pushing their way through 
the skin of the mouth. They are beginning to appear on the 
branchial arches and eeratohyals as well. 
Branchial Apparatus. — (Plate 9.) The branchial appa- 
ratus of Spelerpes shows a marked difference from that of both 
Crytobranchus and Rana. The most noticeable features of the 
branchial cartilages of Spelerpes longicaudus are (a) the absence 
