716 MAMMALIA. 
almost obliterated. The thoracic cavity is separated from 
the abdominal cavity by a partly muscular diaphragm, 
which is supplied by two phrenic nerves, arising from the 
fourth cervical spinal nerves. By its contraction the 
diaphragm alters the size of the thoracic cavity, and thus 
W190 
Fic. 392. —Vertical section through rabbit’s head.—From a section, 
with help from Parker’s Zoofomy and Krause. 
fmx., Premaxilla with incisors ; ,.e., part of mesethmoid partition ; 
Lb. maxillary turbinals; ¢.¢., ethmoidal turbinal ; .e., part 
of mesethmoid ; off, olfactory lobe of cerebrum; /s., pre- 
sphenoid; c.c., position of corpus callosum ; és., basisphenoid 
with depression for pituitary body; cé., cerebellum ; 4.0., basi- 
occipital ; s.c., spinal cord ; 7.f., nasal passage ; gullet; Urs 
trachea; eAg., epiglottis 5 svzx., submaxillary y glane ; 
sf, sublingual salivary gland} 7., tongue; A/., transverse 
portion of palatine ; m., anterior end of mandible. 
shares in the mechanism of respiration. At the top of 
the trachea lies the complex larynx, the seat of the voice 
in Mammals. 
Anteriorly the larynx is supported on its sides and beneath by the 
thyroid cartilage ; behind this lies the ring-like cricoid ; dorsally to the 
cricoid are two small triangular arytenoids, 
