NECTURUS MACULATUS. 405 



The chondrocraiiium consists essentially of a delicate framework which rnns around 

 the entire cranial cavity and with which certain other cartilaginous elements are associ- 

 ated in varying degrees of intimacy of relation. The framework consists in the embryo 

 of a pair of latei'al bars, placed parallel to one another and divisible into an anterior ele- 

 ment, the trabecula, and a posterior, or parachordal element. In the adult these names 

 are retained as designations for the regions coi'respouding to those elements, the trabecu- 

 lar region being that anterior to the otic capsules, while the part associated directly Avith 

 the capsules themselves is the parachordal region. Posteriorly, between the otic capsules 

 the frame is completed by a pair of cartilaginous bands or arches, of which one, the supra- 

 occipital arch,^ passes dorsal to the nerve cord, and the other, the basi-occipital arch, lies 

 ventral to this latter part. Accoi'ding to Miss Piatt, the supra-occipital arch is really the 

 neural arch of a vertebra antei'ior to the atlas, which has fused with the skull to increase 

 its strength. At the anterior end of the skull the frame is completed by the development 

 of an internasal plate which connects the convergent trabeculae. Anterior to this the 

 free ends of the trabeculae are continued a short distance in the form of small rostral 

 processes. 



Of the originally external elements, the two large otic capsules are the most 

 intimately related and are completely fused with the posterior portion of the primary part 

 and thus form tlie largest and most voluminous portion of the chondrocranium. Anterior 

 to these are the semi-detached quadrate cartilages, connected with the sides of the tra- 

 becular frame by a narrow process, the trabeculo-quadrate isthmus. Still farther forward 

 and separated from the latter by an interval in which are situated the eye and its acces- 

 sory organs, appears a pair of distinct cartilages, attached to the trabeculae by connective 

 tissue. These are the ante-orbital processes plainly representing a ruthment of the sub- 

 ocular arch, or pterygo-quadrate process, so enormously developed in the frog and other 

 Anura, an homology suggested by W. K. Parker's term of '' ethmo-palatine process." 



The other cartilaginous parts topographically associated with the chondrocranium are 

 the nasal and optic capsules, of which the former lies directly upon the anterior end of 

 the completed skull, and barely comes in contact with the chondrocranium, while the 

 latter is completely i.solated. These parts will receive separate treatment later. 



The ossifications of the chondrocranium {= "cartilage bones") are few in number in 

 comparison with those of most Urodeles and consist of but four pairs: (1) the quadrates, 

 used to form a strong support for the mandible, (2) the exoccipitals, forming the condyles 



'Miss I'latt objects to the term "occipitale superiius" for the (loi-sal cartilaginovLs arch on the ground that the supra- 

 occipital is not an ampliibian bone and i^refers "interoccipitale," as suggested to her by Gaupp. This term, however, leaves 

 out of account the ventral arch, unless we use the tenns "interoccipitale dorsale " and " interoccipitale ventrale " which are 

 cumbersome and possess the disadvantage of the substitution of new terms for old and readily understood ones. Moreover, 

 a portion of the Amniote supra-occipital is preformed in cartilage, and it seems more than probable that there is at least a 

 partial homology between it and the cartilaginous arch found here. The same may also be saiil of the basi-occipital piece. 



