THE CHONDROCRANIUM IN THE ICHTHYOPSIDA . 99 



process (d) to be described later, passes backwards from 

 the ventral margin of the cup-like anterior end of the 

 capsule. At its posterior end this process fuses laterally 

 with the lamina cribrosa (Z) while medially it terminates 

 in a process projecting freely backward (Fig. 13, vp). 



The cylindrical dorsal process (d) extends diagonally 

 across the anterior end of the olfactory organ from the 

 dorso-median margin of the cup to the anterior end of the 

 lamina cribrosa. A short connecting rod joins the dorsal 

 process and lamina cribrosa with the ventral process in 

 front of the nasal duct (nl). As in the preceding 

 stage, the lamina cribrosa forms a roof over the posterior 

 end of the olfactory organ. It now reaches downwards 

 to meet the outer end of the antorbital process thus en- 

 closing the orbito-nasal foramen {on), and outwards and 

 forwards to meet the ventral and dorsal processes as de- 

 scribed ai)ove. It is perforated near the lateral margin by 

 several small foramina through which pass a branch of the 

 ophthalmicus profundus (rj)) and some small blood ves- 

 sels (b). A branch of the nasalis internus (ni) passes 

 out of the capsule through the foramen in its median wall. 



Desmognathus fusca (Fig. 14). 



The chondrocranium of Desmognathus fusca, of which 

 I have modelled two stages, presents so great a similarity 

 to the earlier stages in Amblystoma that only a few words 

 need be devoted to it. Figure 14 represents the model of 

 the skull of an embryo about twenty mm. long. 



The parachordals (p) are represented by three narrow 

 bands of cartilage ; one extending between the posterior 

 ends of the otic capsules and having the notochord partly 

 imbedded in it, and two other bands which connect the 

 apex of the notochord with the posterior ends of the tra- 

 beculae. 



