THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 103 



lying beneath that portion of the cranial cavity included 

 between the posterior halves of the otic capsules. As 

 before, the notochord projects freely forward in the me- 

 dian line. Laterally and in front the basilar plate merges 

 into the capsular floors and the trabeculfe. 



The otic capsules present essentially the same condi- 

 tions found in stage three of Ambly stoma (Figs. 4-7) 

 except that the otic process of the quadrate is fused with 

 the antero-ventral surface of the capsule. A trabecular 

 crest just large enough to enclose the optic and oculo- 

 motor foramina and to form a point of attachment for the 

 ascending process is now developed. The appearance of 

 simple aiitorbital processes upon the sides of the trabecu- 

 lae is the only further change which needs mention here. 



Third stage. — Larva forty-five mm. long (Fig. 16). 

 A continued fusion of the margin of the occipital process 

 with the wall of the otic capsule, resulting in a reduction 

 of the size of the jugular foramen is the most noticeable 

 change in this region. The synotic tectum is now fully 

 developed and presents the usual form. The basilar plate 

 remains the same as in the previous stage. 



The otic capsules have reached their highest state of de- 

 velopment. The median wall is perforated by four foram- 

 ina which correspond almost exactly to those described 

 for the otic capsule of the fourth stage of Amblystoma 

 (Fig. 11). In iiict the onl}^ differences of any importance 

 between the otic regions of this skull and that described 

 as the fourth stage for Amblystoma are in the absence of 

 the parachordals at the anterior end of the notochord, and 

 the more median position of the foramen for the palatine 

 nerve iiml). A small crest is now developed along the 

 posterior half of the trabecula. A slender connecting rod 

 unites the posterior end of the crest with the opposite wall 

 of the otic capsule. Antorbital processes project outward 

 and forward from the sides of the trabecular. 



