54 ANATOMY OF THE RABBIT. 
closing the aperture for transmission of the spinal cord from the 
cranial cavity. The basisphenoid and presphenoid bear lateral 
expansions, respectively the greater and lesser wings, or ali- 
sphenoids and orbitosphenoids, which assist in the formation 
of the side walls of the brain case. The bone capsule (periotic) 
lodging the internal ear on either side is solidly built into the 
lateral cranial wall between the exoccipital and alisphenoid, while 
further forward the light scroll-like surfaces of the ethmoid bone, 
or ethmoturbinal, representing the chief portions of the nasal 

Fic. 28. Composition of the mammalian skull. Cartilage dotted, cartilage 
bone shaded, derm bones plain. I-XII, cranial nerves; as, alisphenoid; bh, 
body of hyoid; bo, basioccipital; bs, basisphenoid; c, canine teeth; cm, Meckel’s 
(mandibular) cartilage (1); e, mesethmoid; et, ethmoturbinal; ex, exoccipital; 
f, frontal; hy, hyoid (II); i, incisors; 1, lacrimal; m, molar teeth; mn, mandible; 
mx, maxilla; mt, maxilloturbinal; n, nasal; nt, nasoturbinal; os, orbitosphenoid; 
p, premaxilla; pa, parietal; pl, palatine; pm, premolar teeth; pt, pterygoid; 
sq, squamosal; so, supraoccipital; th, thyreohyal (III); v, vomer; z, zygomatic, 
capsule is attached on each side of the base of the mesethmoid 
The original proportions of the nasal capsule are however more 
nearly commensurate with the general cavity of the nose; and 
additional turbinal surfaces, comprising the nasoturbinals and 
maxilloturbinals are attached secondarily to the nasal and 
maxillary bones. 
To this foundation there is‘ added a series of enclosing bones, 
for the most part thin and superficial, but nevertheless making up 
the greater part of the facial portion of the head skeleton as 
opposed to the cranial or brain containing portion. The series 
comprises the interparietal (absent in the hare and many mam- 
