RESPIRATORY AND VOCAL ORGANS. 21 



uro-hyal bone, which passes downwards in front of the larynx, 

 sliding in a sheath ; c c, the appendages of the hyoid bone, 

 covered with the mylo-hyoideus, which, arising from the base 

 of the lower jaw, pulls the hyoid bone, and consequently the 

 tongue, forwards ; d (7, the genio-Jiyoideus, which arises from 

 the lower jaw farther back, and is attached to the end of the 

 apo-hyal bone, so as to draw the tongue forwards and upwards ; 

 the stylo-hyoideus, e e, arising from the back part of the lower 

 jaw, and inserted into the basi-hyal bone, its action being to 

 pull the tongue backwards. Several muscles, however, have 

 been removed, to prevent confusion. Two very slender mus- 

 cles, //, are seen arising from the base of the hyoid bone and 

 the sides of the larynx, continuing downwards in front of the 

 trachea, being attached to the subcutaneous cellular tissue, and 

 finaHy inserted into the edge of the furcula at its angle ; they 

 are the deido-tracheales, of which the action is to contract the 

 skin of the fore part of the neck, pull the tongue downwards, 

 and assist in shortening the trachea. 



The ozsophagus^ g, A, funnel-shaped at its commencement, is 

 seen passing behind the trachea, and coming out between the 

 bronchi, at i, where it is cut off, that the lungs may be seen. 

 The proventriculus^ j ; the stomachy k ; the intestine^ I m n. 



The irackea, ^ P ^i is an elastic tube, commencing behind 

 the tongue, a, where it opens into the throat, and extending to 

 opposite the first rib, where, at the syrinx or inferior larynx, 

 it divides into the two bronchi, r r. It is a little flattened, 

 and is not of equal diameter throughout. Its bony rings, sixty 

 in number, are entire, very thin, elastic, narrowed in the 

 middle in front, and connected by elastic membrane. It is 

 lined with a smooth mucous membrane, and is covered exter- 

 nally with layers of cellular tissue. It is extremely flexible, 

 contractile, and extensile, in order to accommodate itself to the 

 contractions, extensions, and highly diversified motions of the 

 neck. The bronchi, r r, differ from the trachea, in having the 

 rings, about thirteen in number, incomplete, and less flattened, 

 the space left between the extremities of these half rings being 

 occupied by elastic membrane. Let us now examine these 

 parts in detail. 



