THE SKELETON. 27 
nasal cavities removed, and the third should be cut trans- 
versely on a line joining the middle of the orbits. The 
ethmoid is usually visible externally as a small rhomboid 
plate on the medial wall of the orbit between the frontal, 
Yorrer~ 
erences ema . oid} 
ae sepeeiiony ple T 
diy? My 
Fic. 15. DraGRAM OF THE Bones OF THE MAMMALIAN SKULL VIEWED 
LATERALLY. 
I, 2, 3, etc., indicate the places of exit of the twelve cranial nerves. pm, 
Premaxillary; ty, tympanic, 7 and 8 are on periotic; thy, tympano- 
hyal; shy, stylohyal; ehy, epihyal; chy, ceratohyal; bhy, basihyal ; 
thhy, thyrohyal. The cartilage bones are shaded.—(From Flower, 
after Huxley.) 
lachrymal, and palatine bones. It consists of four parts: 
the paired ethmoturbinals or lateral ethmoids (Fig. 18), 
the mesethmoid, and the cribriform plate. The ethmotur- 
binals are in the form of scroll-like laminze which project 
forward from the transverse cribriform plate into the nasal 
cavities. The portion which appears externally in the 
medial wall of the orbit is the os planum. In the recent 
state, the surfaces of these bones within the nasal cavity are 
covered with a mucous membrane over which the first pair 
of cranial nerves (olfactory) are distributed. The delicacy 
