22 TOPOGRAPHICAL ANATOMY OF THE 



carry is for the nutrition of the lung, while tliat borne by the pulmonary 

 artery is concerned with the respiratory function. 



It should be added that, in the horse, the oesophageal branches of 

 the broneho-cesophageal and left gastric arteries contribute small twigs 

 that ramify in the subpleural lung tissue in the neighbourhood of the 

 pulmonary ligament. 



Bronchial lymph glands (lymphglandulse bronchiales), into which 

 the lymphatic vessels of the lungs drain, are grouped about both the 

 dorsal and ventral aspects of the bifurcation of the trachea and the 

 initial part of the bronchi. The dorsal group is frequently continued 

 for a short distance along the ventral border of the oesophagus, while 

 a prolongation of the ventral group may be insinuated between the aorta 

 and the pulmonary artery. A few small glands are contained within 

 the substance of the lung, where they are related to the main bronchus. 



N. PHRENICUS. — The origin of each phrenic^ nerve by roots from 

 the fifth, sixth and seventh cervical nerves is noted during the dissec- 

 tion of the neck. The root from the fifth cervical nerve is very frequently 

 absent, and, when present, is smaller than the other two. 



Both right and left nerves enter the thorax ventral to a subclavian 

 artery, and pass through the precardial mediastinum. Tliey then cross 

 the pericardium ventral to the roots of the lungs. The left nerve 

 continues through the postcardial mediastinum to the diaphragm ; but 

 the right nerve gains that muscle by running along the lateral aspect of 

 the caudal vena cava, and is therefore not contained in the mediastinal 

 septum, but in the special caval fold of pleura. There are also further 

 differences between the relations of the two nerves. The left follows a 

 course along the left aspect of the brachio-cephalic artery and the 

 common brachio-cephalic trunk and then crosses the commencement of 

 the aortic arch and the pulmonary artery, the pericardium intervening : 

 the right nerve lies along the right face of the cranial vena cava. 



The pericardium (Pericardium). — The pericardium- is a fibro- 

 serous sac somewhat loosely enclosing the heart, and, in agreement with 

 the organ it surrounds, is conical in form with the base of the cone 

 directed towards the vertebral column. The apex points towards the 

 sternum and the sternal attachment of the diaphragm. Strong and slightly 

 elastic fibrous tissue, sterno-'pencard,iac ligaments (ligamenta sterno- 

 pericardiaco), fixes the pericardium to the sternum from the level of the 

 fifth rib to near where the diaphragm takes origin from the xiphoid 

 process. The area of attachment is triangular with the apex looking 

 towards the thoracic entrance. The outer face of the pericardium is 



1 (fypnv (pluvn) [(i!r.], the diaphra<,'in, heart, seat of the emotions. 

 - irepi (peri) [Cri'.], around ; KapSia (cariiia) [Gr.], the heart. 



