DISSECTION OF THE DOG 35 



the commencement of the arterial and the end of the venous systems, the 

 oesophagus, the termination of the trachea, the vagi, left recurrent, phrenic, 

 cardiac, and pulmonary nerves. 



The postcardial mediastinum contains the aorta, the azygos vein, the vagi, 

 left phrenic and sympathetic nerves, the thoracic duct, and the oesophagus. 



Abticttlationes sternocostales. — Nine of the thirteen ribs on each side 

 articulate with the sternum by means of their cartilages. The end of the rib 

 cartilage is received into a concavity on the lateral surface of the sternum and 

 articulates therewith by a diarthrodial joint. Each articulation is enclosed 

 by a joint-capsule (capsula articularis) and is provided with a synovial mem- 

 brane. On each side of the joint the capsule is thickened to form the radiate 

 sterno-costal ligaments (ligg. sternocostalia radiata). 



The cartilages of the tenth, eleventh, and twelfth ribs do not reach the 

 sternum, but each is bound by fibrous tissue to the cartilage preceding it. The 

 cartilage of the last rib is generally quite independent of the second last. 



Synchondroses intersternales. — The eight bony segments of the 

 sternum are joined to each other by cartilage, and the union is strengthened 

 by an internal proper sternal ligament (lig. sterni proprium internum). Strong 

 and well marked, the ligament is narrow over the first two or three segments 

 of the sternum, but later it increases in width. 



Dissection. — It will facilitate the further dissection of the thoracic contents 

 if the fragment of the sternum and portions of the last few ribs be removed. 

 This should be done by cutting through the ribs in a fine with the level 

 at which the other ribs were divided previously. The attachment of 

 the diaphragm to the ribs and sternum must be noted and then severed. 



This dissection allows of the examination of the liver, stomach, spleen, 

 and pancreas, which was not readily possible earlier. 



Hepar. — The liver is a large, solid, glandular organ of chocolate colour, 

 closely applied to the abdominal face of the diaphragm. Approximately 

 central in position, it lies partly under cover of the ribs, but generally a 

 considerable proportion of its bulk projects beyond the costal arch. 



The liver may be described as presenting two surfaces and a circumferent 

 edge. The cranial surface is applied closely to the diaphragm and part of the 

 wall of the abdomen, and upon these it is moulded. It is consequently convex 

 in all directions, and, when the organ is in situ, slopes dorso-ventrally and 

 cranialwards in its dorsal half and caudalwards in its ventral half. 



The caudal surface is, in the main, concave ; but, owing to the influence 

 of adjacent hollow viscera, not regularly so. The organs with which it is in 

 contact are the stomach, intestines, pancreas, and the right kidney. The 

 amount of intestinal contact naturally depends largely on the degree of 

 distension of the stomach. 



The margin of the liver is sharp ventrally and laterally, but blunt and 



d 2 



