AIR-TUBES AND LARYNX 



373 



.111, 3rd bronchial ring ; car, carotid artery; j, jugular vein; o.h, hyoid (cut 

 through); thym, thymus ; thyr, thyroid. 



Miwlex and tlu'tr inwrfioH-*: xt.tr, sterno-trachealis ; tr.br.d.b, trach. -bronch. - 

 dorsalis brevis (membrana tympanifonnis interua) ; tr.br.d.l, trach. -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 .11 and 

 pessulus). 



-Y'/-/v.s; e, 1st cervical; c.a, cervicalis ascendens ; c.d.i, c.d.s, cervicalis 

 desceudens inferior et superior; y, glossopharyngeal ; g.c.s, anterior (superior) 

 cervical ganglion; y.p, petrosal ganglion (nearer to y.c.v than shown on 

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

 eervicalis ; *, cervical sympathetic ; r, 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 



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



AL, arytenoids, with an intercalary piece, S l ; JR K, 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 cornu 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 B** 



