152 



THE MUSCLES. 



triangular membranous portions (d) of the diaphragm, one on 

 each side of the spinal column. It is pierced by an opening 

 for the vena cava (f). 



FIG. 74. DIAPHRAGM, CAUDAL SURFACE SEEN OBLIQUELY FROM THE RIGHT. 



a, right cms; b, left crus; f, ^, sternocostal part of diaphragm; d, d' ', membra- 

 nous portions of the diaphragm; e, central tendon; e', prolongations of central ten- 

 don; f, opening for posterior vena cava; g, oesophagus; h, aorta; i, M. transversus 

 abdominis. 



The muscular portion is in two parts: (a) The vertebral 

 portion (a, b} arises by a single tendon from the ventral surface 

 of the second, third, and fourth lumbar centra. The tendon 

 diverges into two, the right one (a) of which is much stronger, 

 and from each of the two arise muscle-fibres. Each mass of 

 fibres is one of the two crura (sing, crus) of the diaphragm. The 

 aorta (//) enters the abdomen between the crura dorsally. The 

 fibres of each crus diverge to be inserted into the central tendon 

 and the dorsal continuation of its horn. The two sets of fibres 

 unite ventrad of the opening of the aorta. Between this open- 

 ing and the central tendon is another opening for the cesopha- 



