74 DISSECTION OF THE DOG 



veins (vv. phrenico-abdominales) ; (7) hepatic veins (vv. hepaticse) ; (8) phrenic 

 veins (vv. phrenicse). 



With the exception of the two last named, all these veins are satellites of 

 the corresponding arteries. The hepatic veins are numerous ; two to four are 

 large, and the rest are small. They join the vena cava as it runs along the 

 diaphragmatic surface of the liver. 



Vv. phrenic^:. — The dorsal part of the diaphragm is drained by phrenic 

 tributaries of the phrenico-abdominal veins ; but a right and a left vein, in 

 addition, open into the vena cava as it pierces the diaphragm. 



Vena azygos. — Almost the whole of the vena azygos has been examined 

 during the dissection of the thorax. It remains for the commencement of the 

 vein in connection with the first and second lumbar veins to be looked for dorsal 

 to the aorta close to the hiatus aorticus. 



Ductus thobacicus. — The commencement of the thoracic duct in the 

 cisterna chyli must also be examined at this stage of the dissection. The 

 cistern is a mere dilatation of the duct and lies to the right of the aorta on a 

 level with the origin of the renal arteries. It occupies a cleft bounded by the 

 aorta to the left, and by the lumbar origin of the diaphragm and the lesser 

 psoas muscle to the right. The cranial vena cava is ventral to the cistern. 

 From the cistern the thoracic duct passes into the thorax to the right of the 

 aorta. 



Sublumbar muscles. — In the sublumbar region there are three muscles : 

 namely, psoas minor, ilio-psoas, and quadratus lumborum, arranged in this 

 order from the middle line outwards. 



M. psoas minor. — The lesser psoas muscle arises from the bodies of the 

 last two or three thoracic vertebrae and from the bodies of the first three or four 

 lumbar vertebrae. Its insertion is into the psoas eminence of the hip bone. 



M. ixio-psoas. — The ilio-psoas muscle consists of two parts : namely, 

 m. psoas major and m. iliacus. Of these the greater psoas muscle alone can 

 be properly examined at present. 



The origin of the psoas major muscle is from the bodies of the last three or 

 four lumbar vertebrse. Its insertion into the lesser trochanter of the femur 

 will be dissected in connection with the thigh. 



M. quadratus lumborum. — This muscle has an origin in common with the 

 psoas minor from the last two or three thoracic vertebrae. It also arises by 

 separate bundles from the last rib and the lumbar transverse processes. Its 

 insertion is into the lumbar transverse processes, and into the ilium in the 

 neighbourhood of the sacro-iliac articulation. 



Dissection. — Some of the lumbar spinal nerves (seven in number) may now 



be examined. Certain derivatives of these are visible without further 



dissection. Between the psoas minor and quadratus lumborum muscles 



k appear the ilio-hypogastric and ilio-inguinal nerves ; and between the 



