THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 101 



processes in front of the narial duct all the parts described 

 for the nasal capsule of Amblystoma are found in approx- 

 imately the same positions in Plethodon with unimportant 

 modifications as to relative sizes. This similarity is even 

 more apparent in older specimens of Plethodon than in 

 the one from which this model was made. The two small 

 foramina in the lamina cribrosa mark the points at which 

 a branch of the ophthalmicus profundus (rj)) enters and 

 leaves the capsule. 



Nectukus maculatus. 



Cope ('89) has placed JVectiirus maculatus with its 

 American relative JSTecturus punctata and the European 

 Proteus in a group together under the name Proteida with 

 the remark that they occupy a position intermediate be- 

 tween the Stegocephali and the Urodela, and differ from 

 the latter mainly in the possession of an intercalary bone. 

 Descriptions of three stages in the development of the 

 chondrocranium of JVecturus maculatus are here given. 



First stage. — The first stage represents the skull of 

 an embryo twenty-one mm. in length, and corresponds 

 approximately to the condition found in Amblystoma at 

 a time a little earlier than that represented in the third 

 stage of the latter (Figs. 4-7). The occipital arch con- 

 sists of two processes extending upward from the sides 

 of the notochord and ending freely above. At their bases 

 they are connected with the posterior ends of the para- 

 chordals. 



The parachordals run forward from the bases of the 

 occipital processes, slightly removed from the sides of the 

 notochord. Between the posterior ends of the otic cap- 

 sules they bend inwards and touch the sides of the noto- 

 chord to which they are attached for a short distance, then 

 curve sharply outward, and, fusing laterally with the cap- 



