Mar,, 1903.] Spelerpes longicaudus. 383 



pact and dense cartilaginous tissue, from which all trace of car- 

 tilage cells has disappeared. 



Meckel's Cartilage —(Plates 8, 9, mc. ) 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- 

 pletel}^ 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 lielow 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 chondrified, can be traced ver}- readily. The two capsules 

 form the side wall of the skull, and indications of their juncture 

 over the top of the brain can 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, therefore, the brain lies exposed above, but is pro- 

 tected laterally by the heavy auditory capsules and ventrally b}^ 

 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 

 dilhculty. 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 Ije seen pushing their way through 

 the skin of the mouth. They are beginning to appear on the 

 branchial arches and ceratohyals 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 noticeatJe features of the 

 branchial cartilages of Spelerpes longicaudus are (^a ) the absence 



