THE NECK. 173^ 



stomach whicli is said to prevent vomition in the horse except 

 under extreme circumstances ; others attribute it to the 

 mode of entrance of the oesoj^hagus into the stomach, 

 while some argue the presence of a special spiral valve. 

 This mucous membrane is similar in structure to that of the 

 pharynx and to the cuticular portion of the mucous lining 

 of the stomach, with which it is continuous anteriorly and 

 posteriorly respectively. 



In the upper and anterior part of the neck, perceptible 

 on manipulation in the living animal, is the larynx, a 

 remarkable cartilaginous organ the seat of the voice ; the 

 upper part of the trachea specially modified. It is com- 

 posed of several pieces of cartilage, which are united 

 together in some places by synovial, in others by fibrous 

 articulations. Elastic expanded ligaments in some situa- 

 tions strengthen the connection. The larger cartilages are 

 five in number ; thyroid, cricoid, two arytenoids, and epi- 

 glottis. The Thyroid is the largest, and consists of a body 

 and two wings. The body is supero -anteriorly placed, and 

 is the thickest portion of the cartilage. It has two surfaces, 

 anterior and posterior, and four margins, superior, inferior, 

 and two lateral. To the internal surface the epiglottis is 

 attached by elastic tissue, the external surface is in contact 

 with the sterno-thyro-hyoidei muscles. To the superior mar- 

 gin is attached the thyro-hyoid ligament, to the inferior mar- 

 gin the crico -thyroid ligament, and the aloi or ivings arise from, 

 the two lateral margins. The aloi are firm flat portions of the 

 cartilage which exhibit a tendency to undergo ossification ; 

 each of them manifests the form of an oblique-angled paraL 

 lellogram, the anterior acute angle of which blends with the 

 body of the cartilage ; the postero-inferior acute angle is 

 rather elongated, and presents a synovial surface for articu- 

 lation with the antero-inferior synovial facet of the cricoid 

 cartilage. The postero-superior oblique angle presents a 

 flexible cartilaginous prolongation, superior cornu of the 

 posterior margin, the free extremity of which is united by 

 fibro-cartilaginous tissue to the posterior extremity of the 

 heel process of os hyoides. The antero-inferior oblique angle 

 forms the point of junction of the anterior and inferior 

 margins, to both of which is attached the crico-thyroid 

 ligament. The superior margins of the two alse are con- 

 nected together by the superior extremity of the body and 

 from the whole ridge thus formed the thyro-hyoid ligament 



