96 BULLETIN OF THE ESSEX INSTITUTE. 



the capsule, is the only line of demarcation between the 

 otic and palato-basal processes. A large chamber is en- 

 closed between the posterior end of the trabecula, the 

 anterior end of the capsule and the bars connecting them 

 dorsally and ventrally. The ascending process of the 

 quadrate passes across its external surface, separating a 

 dorsal and a ventral foramen. The Gasserian ganglion 

 occupies this chamber and from it pass out the ramus 

 ophthalmicus profundus {rp) through the ventral fora- 

 men, and the rami ophthalmicus superficialis (/"«), maxil- 

 aris (rm), and mandibularis {m), through the dorsal 

 foramen. 



The foramina by which the rami of the seventh nerve 

 leave the otic capsule are unchanged, except that now 

 there are two upon each side and that they are consider- 

 ably reduced in size. The fenestra ovalis {fo) is now 

 nearly filled by the stapes (s) , which has a slight promi- 

 nence directed outwards and upwards from the antero- 

 dorsal angle of the cartilage towards the otic process of 

 the quadrate. These cartilages, however, do not become 

 united at a^ay time during the development of Amblystoma 

 as they do in some other forms. 



The trabeculse {t) are of nearly uniform size from their 

 junction with the parachordals to the point where they 

 meet in front in the ethmoid plate (e). Optic and ocu- 

 lomotor foramina are of equal size, both being small. The 

 ethmoid plute (e) , arising by the fusion of the anterior ends 

 of the trabeculse in the median line, forms a continuous 

 floor beneath the anterior end of the cranial cavity, the 

 nasal septum {ns) and portions of the olfactory organ. 

 In front it terminates upon each side in a conical process. 

 Laterally a freely ending process (c) extends backwards 

 along the ventral surface of the olfactory organ. This 

 and the adjacent parts of the ethmoid plate are develop- 



