No. I.] SKELETAL ANATOMY OF AMPHIUMA. 15 



atlas. On each side, at the base of the oondyles, are the fo- 

 ramina for the vagus and the glossopharyngeal nerves. The 

 occipital condyles are invested with a thin ectostosis, which 

 continues as far forward as the foramina mentioned. This is 

 the only cartilage-bone that is found in the skull, except that in 

 the hyobranchial apparatus, soon to be described. 



In the supraoccipital region, there is a narrow strip of carti- 

 lage which arises from the posterior end of the otic capsule, and 

 extends inward toward the middle line, but it lacks much of 

 reaching the corresponding cartilage of the other side. Along 

 its upper surface, therefore, the brain, from one end to the 

 other, has no other protection than that of the integument. 



The otic capsules are large, well-developed, and of a long- 

 ovoidal form. They occupy about one-third of the total length 

 of the cartilaginous skull. The upper surface is somewhat flat- 

 tened, and slopes outward and downward. Anteriorly they pass 

 by a narrow band of cartilage into the upper edge of the tra- 

 beculae in front of the foramina for the fifth pair of nerves. 

 Behind, each capsule is rounded, and in the angle between it 

 and the projecting condyle, is found the vagus ganglion. The 

 membraneous canals are well-developed, and may be seen through 

 the walls of the capsule. They are enclosed within correspond- 

 ing cartilaginous canals. On the outer wall of the capsule is 

 found the large fenestra ovalis. It is partially occupied by the 

 cartilaginous stapes, as shown in Fig. 4. All round this stapes 

 is a tract of membrane, except anteriorly, where it is articulated 

 to the otic wall. This stapedial cartilage is confluent with the 

 hinder end of the columella, which will come up for considera- 

 tion in its place. With the exception of the fenestra ovalis, 

 there is no interruption in the cartilage of the outer wall of the 

 otic capsule. The facial foramen lies immediately in front of 

 the fenestra ovalis. At the anterior end of the capsule, and on 

 the lower floor, is found the entrance of one portion of the audi- 

 tory nerve into the labyrinth. Farther back, about opposite 

 the fenestra ovalis, there are three openings in the cartilage of 

 the mesial wall of the otic capsule. The smaller one, high up, 

 is for the passage of the ductus endolymphaticus into the brain- 

 cavity. A second larger foramen in the cartilage, immediately 

 below the last mentioned, admits into the labyrinth the branch 

 of the auditory nerve going to the sacculus and lagena. This 



