434 
Proceedings of Royal Society of Edinburgh. [sess.. 
of the faint furrow apparently represented the ridge : this surface 
ended in a sharp border which bounded the mouth of the bulla. 
The inner surface curved to the opposite side of the mouth, formed 
a rounded obtuse border, which was divided by a shallow de- 
pression into an anterior and a posterior lobe. The anterior end of 
the tympanic opened into the cavity of the bulla and was bounded 
by a strongly curved smooth border. 
The petrous bone articulated with the mastoid-like element close 
to the constricted neck by a smooth plate of bone. The petrosal 
was 28 mm. long and 19 mm. in greatest breadth. Two distinct 
foramina were in the wall which bounded internally the cavity 
of the tympanum, but the stapes was not attached to the boundary 
of the foramen ovale. The internal auditory meatus was distinct, 
and its wall was cribriform for the transmission of the branches of 
the auditory nerve. 
For a number of years I have collected, as opportunities offered, 
the tympanic and petrous bones of the Cetacea, and I have 
presented the specimens to the Anatomical Museum of the 
University. In supplement to the description of their characters 
in the Physeterinae, I may record the measurements and state some 
of the most salient points connected with these bones in the 
Odontoceti now (with the exception of Kogia) in the Collection. 
Tympanic. 
Petrosal. 
Length. 
Breadth. 
Length. 
Breadth. 
Physeter macrocephalus, . 
mm. 
62 
mm. 
48 
mm. 
65 
mm. 
39 
Kogia breviceps, 
30 
18 
28 
19 
Hyperoodon rostratus, . 
57 
43 
64 
44 
Ziphius cavirostris, 
Mesoplodon bidens (Sowerby), 
59 
38 
58 
36 
45 
31 
46 
25 
,, layardi, 
Platanista. gangetica, 
45 
32 
48 
34 
54 
26 
Monodon monoceros, 
51 
27 
55 
28 
Phocoena communis, 
29 
18 
30 
14 
Globicephalus melas, 
48 
33 
45 
30 
,, macrorhynchus, 
45 
22 
40 
29 
Grampus griseus, . 
Lagenorhynchus albirostris, . 
43 
24 
39 
26 
34 
21 
27 
21 
clanculus, 
28 
17 
31 
22 
Delphinus delpbis, . 
31 
18 
29 
19 
,, tursio, . 
39 
25 
42 
24 
