RESPIRA TOR Y S YSTEM. 



655 



nerves, arising from the fourth cervical spinal nerves. By 

 its contraction the diaphragm alters the size of the thoracic 

 cavity, and thus shares in the mechanism of respiration. 

 At the top of the trachea lies the complex larynx, the seat 

 of the voice in Mammals, 



Fig. 287. — Vertical section through rabbit's head. — From a section, 

 with help from Parker's "Zootomy" and Krause. 



;«.r., Premaxilla with incisors ; m.e. t part of mesethmoid partition ; 

 t.b., maxillary turbinals ; e.t., ethmoidal turbinal ; m.e., part 

 of mesethmoid ; olf.l. , olfactory lobe of cerebrum; fo., pre- 

 sphenoid ; c.c, position of corpus callosum ; bs., basisphenoid 

 with depression for pituitary body ; cb. t cerebellum ; b.o., basi- 

 occipital ; s.c, spinal cord ; «./., nasal passage ; g. i gullet ; tr. t 

 trachea ; epg., epiglottis ; smx., submaxillary salivary gland ; 

 s.l., sublingual salivary gland; T. t tongue;//., transverse 

 portion of palatine ; mn., anterior end of mandible. 



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. 



Within the larynx there are stretched membranous bands — the vocal 

 cords. Beside the larynx is the paired thyroid gland. 



Excretory system. — This includes the blood-filtering 



