Terry — The Nasal Skeleton of Amblystoma punctatum. 99 



of the cranial wall. Here a thin membrane extends dorsad 

 from the trabecula to the roof bones and from the cephalic 

 edge of one crista forward and across the middle line in front 

 of the brain to become continuous with the same sheet of the 

 opposite side. In the dorsal part of this membrane there is 

 present a small rod of cartilage (Col. eth.) running in the 

 long axis of the head and therefore parallel with the trabe- 

 cula, its anterior end just dorsad of the above mentioned 

 medial process, its caudal extremity over the olfactory nerve. 

 The little column of cartilage projects laterally among the 

 loosely disposed cells of the perirhinal tissue, and faces me- 

 dially the olfactory bulb. 



The anlage of this independent cartilage appears in the 

 12mm. embryo as a group of closely arranged, oval cells 

 (Fig. 5, Anl.) between which and the end of the trabecula, and 

 connecting the two, is a column of large cells of irregular 

 forms. This column reaches the anterior end of the anlage of 

 the rod passing in front of the olfactory nerve (Fig. 5, C). 



Stage II. 

 Amblystoma 17mm. Figs. 2, 6 and 7. 



The nasal sacs now project about one-fourth of their 

 length in front of the brain so that an Internasal Space 

 can be spoken of ; brain and sac reach the same level vent- 

 rally. The groove on the side of the main nasal sac is wide 

 and deep and is limited below by the now prominent Jacob- 

 son's organ. 



The trabeculae (Tr.) are connected by a narrow Anterior 

 Trabecular Plate (Ant. tr. pi.), the ethmoid plate of 

 Winslow's description, beyond which they extend to the 

 level of the ends of the nasal sac, separated by an inter- 

 trabecular notch. The Crista trabeculae (C. tr.) is high, 

 reaching half way up the side of the brain and presenting 

 a straight cephalic margin ; it is still caudad of the olfactory 

 bulb. The trabecular horn (Co. tr.), broad at its origin 

 at the trabecula, is directed laterad and caudad and is hoi- 



