DISSECTION OF THE DOG 71 



and lesser splanchnic nerves are to be sought bending round the dorsal 

 border of the diaphragm, between this and the psoas minor muscle. 



N. splanchnictjs majoe. — The greater splanchnic nerve arises from the 

 twelfth thoracic sympathetic ganglion, enters the abdomen between the 

 lumbar part of the diaphragm and the psoas minor muscle, and joins a small 

 ganglion dorsal to the coeliac ganglion. 



N. splanchnicus minor. — The lesser splanchnic nerve may be double, or 

 even treble. It leaves the last thoracic and first lumbar ganglia, and ends in a 

 plexus about the adrenal gland. 



Diaphragma. — The diaphragm forms a dome-shaped, muscular, and 

 tendinous partition between the cavities of the thorax and abdomen. Viewed 

 from the abdominal side, it is concave in all directions, and a little more so on 

 the right than on the left. The partition, as a whole, has a marked slope 

 in a ventral and cranial direction. 



The diaphragm is described as consisting of a tendinous centre around 

 which are grouped lumbar, costal, and sternal muscular portions. 



Centrum tendineum. — The tendinous centre of the diaphragm of the dog 

 is relatively small in extent and ventral in position. In outline it is some- 

 what heart-shaped with the base dorsal ; and has a curved continuation from 

 each side of the base running in a dorsal direction towards a tendinous area 

 separating the lumbar and costal muscular parts of the diaphragm. 



Pars lumbalis. — The lumbar part of the diaphragm consists of muscular 

 fibres arising from two tendons. The right tendon, the thicker and 

 stronger, is attached to the bodies of the third and fourth lumbar vertebrae. 

 The thinner left tendon generally arises from the body of the third lumbar 

 vertebra only, though it may have attachment to the fourth vertebra also. 



Each tendon divides into a medial and a lateral portion. The medial divisions 

 of the two tendons unite ventral to the aorta, and thus form an arch over 

 which this vessel passes. The two lateral divisions — slenderer than the medial 

 — are attached to the transverse processes of the first lumbar vertebra. In 

 this way three tendinous arches are produced, and from them right and 

 left muscular fibres spring. These, when followed into the main part of the 

 diaphragm, are found to decussate both dorsal and ventral to the opening by 

 which the oesophagus gains the abdomen. 



Pars costalis. — The costal part of the diaphragm arises from the ribs, from 

 the eighth to the thirteenth, close to the point of union of their bony and 

 cartilaginous segments. It is, therefore, evident that the diaphragm is not 

 attached to the costal margin itself, but slightly within it. 



Pars sternalis. — The sternal origin of the diaphragm is from the xiphoid 

 process and the adjacent part of the sternum. 



Openings in the diaphragm. — There are numerous openings in the diaphragm, 

 but most of them are of small size and of little importance. Three openings, 



3? 4 



