ATR-TUBES AND LARYNX 



373 



ll.III, 3rd bronchial ring ; car, carotid artery ; ./, jugular vein ; o.li, hyoid (out 

 through) : thyni, thymus ; thi/r, th}'roid. 



Muscles and their insertions: st.fr, sterno-trachealis ; fr.br.rl.1t, trach. -bronch. - 

 dorsalis brevis (membrana tympaniformis interna) ; tr.br.d.l, traeh. -bronch. - 

 dorsalis longus (dorsal end of B.I I) ; tr.br. o, trach. -bronch. -obliquus (ventral 

 end of .111); tr.br.r, trach. -bronch. -ventralis (ventral end of B. II and 

 pessulus). 



Nerves :v, 1st cervical; c.u, cervicalis ascendens ; c.d.i, c.d.x, cervicalis 

 descendens inferior et superior; g, glossopharyngeal ; g.c.x, anterior (superior) 

 cervical ganglion; g.p, petrosal ganglion (nearer to </.<.* than shown on 

 figure) ; h' and h", 1st and 2nd root of hypoglossal ; p.c, cervical plexus ; r.c, 

 cervicalis; s, cervical sympathetic ; v, vagus. 



larynx of Monotremes, and especially of Echidna, exhibits a much 

 more primitive condition than that of other Mammals. In these, 

 the thyroid is unpaired, its two halves uniting ventrally, though 



B 



Tr 



C 



JiK 



Ti 



FIG. 279. LARYNX OF ECHIDNA. (A, ventral, B, lateral, and C, dorsal view.) 



AL, arytenoids, with an intercalary piece, S 1 ; RK, cricoid, with a dorsal 

 intercalary piece, S ; SK, skeletal element which is partially subdivided 

 into two portions ventro-laterally ; of these the anterior (t) corresponds to 

 the greater cor mi of the hyoid of other Mammals (that is, to the 3rd 

 visceral arch), and the posterior (*) gives rise to the anterior thyroid element 

 ( = 4th visceral arch); SK', the posterior thyroid element ( = 5th visceral 

 arch), with a basal piece or copula (c) ; Tr, trachea ; ZB, body of hyoid 

 (= copula of 2nd and 3rd visceral arches) : ZH, lesser cornu (-2nd visceral 

 arch). 



still showing traces of its primary paired nature. This shield- 

 shaped thyroid becomes separated from the hyoid, and surrounds 

 the lateral and ventral regions of the larynx, overlapping the 

 cricoid above, 1 and serving as a point of origin and insertion for 

 important intrinsic and extrinsic muscles. 



1 The cricoid may be complete or incomplete ventrally, and its dorsal portion 

 usually forms a broad plate with which the arytenoids are articulated (Figs. 280 

 and 281). The latter, growing out dorsally, may each give rise to a distinct 

 corniculate cartilage (cartilage of Santorini). 



B K** 



