508 Dr. A. A. Gray. On the Anatomical [June 1, 
measurement of the length of the cochlea appears to be so great relatively to 
the same measurement in the bird is owing to the fact that, in the reptile, 
the oval window is situated in the vestibule, while in the bird it is placed 
some little distance along the tube of the cochlea. 
The vestibule measures 3°75 mm. in its greatest diameter, and the major 
axis of the oval window is nearly 1:5 mm. in length. 
The superior canal measures 4°5 mm. in internal, and 6°5 mm. in external 
diameter. The greatest distance of the canal from the vestibule is 1:5 mm., 
and the diameter of the canal itself is 1 mm. The posterior canal has 
internal and external diameters of 4 mm. and 6 mm. respectively. The 
greatest distance of the canal from the vestibule is 0°5 mm., and the 
diameter of tke canal itself is 0°75 mm. 
The horizontal canal measures 3 mm. in internal, and 5 mm. in external 
diameter. The greatest distance of the canal from the vestibule is 1 mm., 
and the diameter of the tube of the canal itself is 0°75 mm. ; 
In its general shape the labyrinth of the monitor resembles those of other 
reptiles ; that is to say, it 1s roughly pyramidal. The canals do not present 
such a constantly curved outline as do those of the bird and the mammal, 
and in this respect also they are more like those of other reptiles. The 
perilymph space is well marked in the canals. The horizontal canal, h., has 
no communication with the posterior canal, p., at the point at which they 
cross, the monitor resembling the gecko in this respect and differing from all 
the other reptiles examined by the writer. There is no bridge connecting 
the upper surface of the saccule with the middle of the superior canal 
in the monitor, such as was found in the teguixin and the West African 
python.* 
The vestibule in the monitor is very similar to that found in other 
reptiles, and needs but little remark. The saccule forms by far the larger 
portion of the vestibule. It is roughly cone-shaped, with the apex of the 
cone near the junction of the superior and posterior canals. It contains, and 
is almost entirely filled by, the large otolith mass, 0.s., which consists in this, 
as in other reptiles, of a collection of innumerable minute crystals held 
together by a semi-gelatinous envelope. The saccule is external to the 
utricle. The last-named cavity is very small, and is really only large enough 
to receive the openings of the three canals. 
The oval window, /o., is situated at the lower and posterior portion of 
the saccule. It is oval in shape, resembling that of the mammals rather 
than that of other reptiles and birds. It is, indeed, a narrower ellipse than 
is found in the case of some mammals, such as the echidna and the 
* Gray, op. cit., vol. 2, pp. 214 and 222. 
