28 ILLINOIS BIOLOGICAL MONOGRAPHS [28 



and the verticale, the lamina medialis is pierced by two foramina, through 

 the dorsal of which, the nasalis internus of the profundus nerve passes to 

 the intermaxillary gland; while a blood vessel passes through the more 

 ventral one. A small prenasal process extends anteriorly a short distance 

 from the median ventral surface of the cupola. The internasal space is 

 deep and narrow, and it is filled with intermaxillary glands which extend 

 back beneath the planum basale, to its posterior margin. In the presence 

 of these glands, Plethodon differs from Cryptobranchus and Spelerpes 

 but resembles Amblystoma and Salamandra. 



In all essentials Plethodon resembles very closely the adult Amblystoma 

 to which it is probably nearly related. The absence of earlier stages has 

 prevented a study of the development of the capsule; but comparing the 

 single larval stage of Winslow with my early stages of Amblystoma, 

 coupled with the many resemblances between the adults, I am inclined to 

 place Plethodon very near to Amblystoma. The absence of the fenestra 

 infra-conchalis in Plethodon is the primary difference between these cap- 

 sules; but the position and size of the planum verticale, the lamina externa 

 and medialis, the anterior cupola as well as the large dorsal and ventral 

 gaps are resemblances that suggest a very close relationship between these 

 animals. 



NECTURUS MACULATUS 



As in Spelerpes, the chondrification of the nasal capsule of Necturus 

 is greatly retarded; so that, except for the mere extension of the trabeculae 

 into the head region, there is no evidence of a nasal skeleton up to the 25 

 mm. stage. In higher Urodeles of this size, well developed capsules are 

 already chondrified. 



In a 24 mm. larva, the trabecular crests are not developed, and the 

 cylindrical trabeculae incline toward each other, but do not unite to form 

 the planum basale. There is no evidence of a cornu at the anterior end, 

 nor has the antorbital process yet chondrified; but procartilage cells have 

 formed near the trabecula which indicate its later development. The 

 forebrain lies lateral to the nasal sac and extends slightly anterior to the 

 trabeculae. 



In a slightly older stage (Fig. 25), the anterior ends of the trabeculae 

 more closely approach each other and near the tips they have expanded 

 dorso-laterally, so that a cross section of the trabecula in this region is 

 reniform. Miss Platt (1897) has described the independent chondrifica- 

 tion of the planum basale, and its subsequent connection to the trabecula; 

 although this stage does not show the chondrified basale, yet a few pro- 

 cartilage cells lying in the tissue between the anterior ends of the trabeculae 

 indicate its origin as independent of the trabeculae. In this stage also, a 

 small triangular antorbital process has chondrified from the trabecula. 



