520 RESPIRATORY SYSTEM OF THE HORSE 
The arytenoideous transversus (M. arytnoideus transversus) is an unpaired 
muscle which stretches across the concave dorsal surface of the arytenoid cartilages. 
Its fibers are attached on either side to the processus muscularis and the ridge which 
extends forward from it. The right and left parts of the muscle meet at a fibrous 
raphé, which is connected with the transverse arytenoid ligament. Fibers of the 
ventricularis muscle overlap its anterior part. It narrows the rima by draw- 
ing the arytenoid cartilages together (adduction). 
The ventricularis! lies in the lateral wall of the larynx, covered by the lamina of 
the thyroid cartilage. It arises from the anterior part of the crico-thyroid membrane 
and the ventral border of the thyroid lamina. Its fibers pass upward and backward 
=e ~ Root of tongue 
Soft palate (cut) 
Salpingo-pharyngeal 
fold 
Epiglottis 
Wall of pharynx 
Aryleno-epiglottic Arytenoid cartilage (apex) 
fold 
Posterior pillar of soft palate 
Position of cricoid 
cartilage under asophagus 
Thyroid gland 
Trachea 
7 (Esophagus 
Fig. 463.—Apitus Larynots oF Horse, Exposed BY OPENING PHARYNX AND BEGINNING OF (EsoPpHAGUS ALONG 
Mepian Dorsau LINE. 
1, False vocal cord; 2, lateral ventricle; 3, true vocal cords; 4, rima glottidis. 
to end partly on the processus muscularis, partly on the arytenoideus transversus, 
meeting its fellow. 
The vocalis! is also medial to the lamina of the thyroid cartilage, and is in part 
separated from the preceding muscle by the laryngeal saccule. It has an extensive 
origin on the crico-thyroid membrane. Its direction corresponds with that of the 
true vocal cord. It is inserted into the lateral surface of the arytenoid cartilage 
below the processus muscularis. 
The two preceding muscles close the rima glottidis and slacken the vocal cords. 
With the arytenoideus transversus and crico-arytenoideus lateralis they form a 
sphincter which closes the entrance to the larynx. | 
1 These two muscles were formerly taken together as parts of the thyro-arytenoideus muscle, 
! 
