140 EQUINE ANATOMY. 



THORAX. 



This cavity is bounded in front by \\\^ first ribs and longus colli, 

 and has passing through this opening lymphatic glands ^ trachea, 

 oesophagus, axillary and carotid vessels, anterior cava, tenth, sy??i- 

 pathetic, inferior laryngeal and phrenic iierves ; behind, by the dia- 

 phragm; above ^ the vei'tebrce, ribs, longus colli, thoracic duct, aorta, 

 vena azygos and sympathetic ; below, by sternum, costal cartilages 

 and the triangularis sterni ; laterally, by ribs and deep intercostal 

 muscles. 



The contents are heart and great vessels, lungs, oesophagus, 

 trachea, nerves, thoracic duct, etc. 



THE MEDIASTIN^. 



The portion of the thorax in front of the heart is called the an- 

 terior mediastinum, that behind, the posterior. The former con- 

 tains the trachea, oesophagus, anterior aorta and divisions, anterior 

 cava, thoracic duct, tenth, cardiac, recurrent and phrenic nerves, 

 and thymus gland in young animal. 



The latter contains the posterior aorta, vena azygos, thoracic 

 duct, oesophagus, tenth and left phrenic nerves, and hgamentum 

 latum. 



Ductless Glands. 



Spleen, see Abdome?i ; supra-renal bodies, see Kidney ; pituitary 

 gland, see Brain. 



THYROID GLAND. 



The thyroid is a gland lying in the neck under the first two 

 tracheal rings, composed of two lateral lobes, a right and left, 

 united by a median portion, the isthmus. 



Structure. 



Fibrous coat, which covers it, and sends in prolongations, as in 

 the spleen. 



Parenchyma. — This is divided into lobules, which contain round 

 vesicles, lined with polygonal cells, and containing albuminous 

 matter. 



Vessels. 



Thryo-laryngeal. 



Ne7-ves. 



First and second cervical and sympathetic. 



