THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 109 



basilar plate of Amblystoma (Figs. 9 and 10 p), form 

 a more or less complete floor beneath the otic portion of 

 the brain cavity. The otic capsules are approximately 

 oval in shape and in all cases have a median wall distinctly 

 separating the cavity of the capsule from that of the brain. 

 There are generally four foramina in this wall through 

 which pass the seventh and eighth nerves and the endo- 

 lymphatic and perilymphatic ducts. In the ventro-lateral 

 wall of the capsule there is a large fenestra ovalis which 

 may or may not be occupied by a stapes. When present 

 the stapes appears first at the anterior end of the fenestra 

 and only later, if at all, does it reach back to the posterior 

 wall of this aperture. The stapes may be connected with 

 the quadrate by a stapedial process. 



Trabeculse, either slender rods with barely enough crest 

 to cover in the optic and oculomotor foramina as in Des- 

 mognathus, or solid beams as in Amblystoma, connect the 

 parachordals and otic capsules with the nasal capsules. 

 At its posterior end there are two places at which each 

 trabecula joins the cartilages of the otic region. Of these 

 points of fusion, the ventral, joining the hixae of the tra- 

 becula with the parachordal, is formed early, while the 

 dorsal, joining the trabecular crest with the otic capsule, is 

 a later occurrence. Anteriorly the trabeculte usually bend 

 inward, and, fusing in the median line into an ethmoid 

 plate, take part in the formation of somewhat complex 

 nasal capsules. But here, again, Desmognathus, with 

 nothing more complex than cornua trabecula3 (Fig. 14, c), 

 proves an exception to the general rule. 



An antorbital process projects outward and forward 

 from the side of the ventral margin of the trabecula be- 

 hind the olfactory organ. In some forms it later fuses 

 with the other parts of the nasal capsule. The variety 

 of forms .shown by the nasal capsules of the different 



