THE CHONDROCRANIUM IN THE ICHTHYOP8IDA. 105 



another specimen from the same lot of embryos was also 

 described and figured by Professor O. P. Hay in his paper 

 of '90. 



First STAGE. — (Figs. 17-18) . — The occipital processes 

 have fused with the otic capsules and their distal ends project 

 inward over the sides of the cranial cavity as the first steps 

 in the formation of the synotic tectum. The parachordals 

 (Fig. 18, jp) extend forward from the bases of the oc- 

 cipital processes, and, after curving inward to the sides 

 of the notochord and fusing beneath it, they each divide 

 into a median and a lateral band. The lateral bands of 

 the two sides curve outward and, fusing with the capsular 

 floors, pass forward to the posterior ends of the trabeculae. 

 The median bands separate in front of the apex of the 

 notochord, bend laterally and join the lateral bands again 

 at their junction with the trabeculae. Between these two 

 parts of each parachordal a fontanelle is enclosed. 



The otic capsules present nearly the same condition as 

 that found in the fourth stage of the skull of Amblystoma. 

 But here, as was also noted in Necturus, the foramen for 

 the palatine branch of the seventh nerve {pal) is on the 

 median side of the median capsular wall. 



The trabeculae extend from their union with the para- 

 chordals forward to the nasal region , where they fuse in a 

 small ethmoid plate which is terminated anteriorly by two 

 broad triangular cornua. Along the middle and posterior 

 end of each trabecula is a well-developed crest covering 

 in the optic and oculomotor foramina as usual. It is con- 

 nected postero-dorsally with the anterior end of the otic 

 capsule, and it is also connected with the median angle of 

 the quadrate by means of the ascending process («/>). The 

 point at which the ascending process joins the trabecula is 

 relatively farther anterior in Amphiuma than in Amblys- 

 toma, thus producing more elongate foramina for the exit 



ESSEX INST. BULLETIN, VOL. XXVm 7* 



