i8 
RICHARDS. 
supplementary to those of Dr. Buck, as being — thanks to 
the photographer — a clearer view, and, finally, as especially 
illustrative of points particularly touched upon in this 
paper. Among the latter I wish to call especial attention 
to the great mass of leathery ?f soft parts*' here seen on sec- 
tion as detached from the upper, and still closely and inti- 
mately adherent to the lower half of the posterior external 
aspect of the skull. The reader will please observe how 
this tissue dips into the deep fossa below the mastoid tip and 
how far (even as thus seen only along the line of section) 
it serves to mask the existence of the mastoid eminence. 
I can again assure him that the removal of this tissue, 
comprising the periosteum, from the fossa in question, 
from around the cartilaginous stump corresponding to the 
human styloid process, and from the mouth of the stylo- 
mastoid foramen, was a work calling for the expendi- 
ture of much time and occasionally of considerable 
physical force. Cross sections of four (and at the 
top of the specimen of part of a fifth) mastoid cells 
are seen in the picture close to the posterior surface 
of the skull. The* fibrous mass of tissue seen running 
almost vertically upwards from the upper part of the 
secondary tympanic cavity occupies a groove which 
marks the position and course at this point of the^ suture 
intervening between the mastoid prominence of the ex- 
occipital and the bony process interposed between this 
prominence and the pars petrosa of the periotic. viz., the 
occipito-squamosal part of the occipito-squamoso-periotic 
suture. On the anterior surface of the pars petrosa at a 
point about half-way down the front (left hand) border of 
the specimen is seen the bundle of fibres comprising the 
facial and auditory nerves. On a horizontal line drawn 
backwards between this bundle of fibres and the lowest 
of the five visible mastoid cells we see the narrowest 
portion, or isthmus, of the secondary tympanic cavity, 
