152 THE MUSCLES. 
triangular membranous portions (¢) of the diaphragm, one on 
each side of the spinal column. It is pierced by an opening 
for the vena cava (/). 
Fic. 74,—DIAPHRAGM, CAUDAL SURFACE SEEN OBLIQUELY FROM THE RIGHT. 
a, right crus; 4, left crus; ¢, ¢’, sternocoslal part of diaphragm; d@, @’, membra- 
nous portions of the diaphragm; ¢, central tendon; e’, prolongations of central ten- 
don; 7, opening for posterior vena cava; g, cesophagus; %, aorta; 7, M, transversus 
abdominis. 
The muscular portion is in two parts: (a) The vertebral 
portion (a, 4) 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) ofthe 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- 
