186 THE AMERICAN NATURALIST. (VoL. XXXIV. 
were not, after dissection, selected on account of the abnormal- 
ities which they presented. 
NUMBER 
oF CASES 
TYPES. OBSERVED 
— 
. PERSISTENT POSTERIOR CARDINAL VEINS (Vv. Cardinales fost.). 
(a) Left common iliac vein (V. iliaca communis sinistra) absent. 3 
(4) Left common iliac vein (V. iliaca communis sinistra) present. 2 
2. THE COMMON ILIAC VEINS (V. iliaca communis sinistra and 
dextra) UNITE TO FoRM THE POSTCAVAL VEIN OPPOSITE 
THE MIDDLE OF THE SIXTH LUMBAR VERTEBRA, WHICH 
Is CONSIDERABLY CEPHALAD OF THE NORMAL POINT OF 
JUNCTION (opposite the posterior half of the seventh). The 
ilio-lumbar veins also, in each case, open into the right and 
left common iliacs and not into the common postcava, as is 
usually the case in the cat. . 3 
3. THE MIDDLE SACRAL VEIN (V. PS media] AND ITS Re 
LATION TO THE VEINS OF THE PELVIC REGION. 
(4) Opens into the right common iliac vein Su iliaca LATTE 
dextra ‘ 4 
(4) Opens into angle of union at two veins p bit join veins üt 
right and left aas — à è à i 
4. PERFORATION OF A VEIN 
(a) An artery j 6 
(4) A nerve 3. 
5. DOUBLE VEINS WHERE Di IS Ness PxsstKT 7 
33 
Description of the Venous Abnormalities. 
I. PERSISTENT POSTERIOR CARDINAL VEINS (Vv. Cardinales 
post.). — Our knowledge of the development of the postcaval 
vein and our interpretation of the significance of the persist- 
ent double postcaval veins are largely due to Hochstetter,! who 
has shown that these veins are the homologues of the posterior 
cardinal veins of the embryo: and of lower vertebrates. 
Wilder and Gage? state that double postcaval veins occur in 
the domestic cat once in about ten cases. This percentage is 
somewhat less than that found by the writer (20 per cent), but 
perhaps represents more accurately the conditions commonly 
met with. In either case the percentage is extremely large when 
we consider how rarely this abnormality is met with in man. 
1 Hochstetter. Anat. Anz., Bd. ii, Morph. Jahrb, Bd. xiii, and Anat. Anz. 
Bd. iii. 2 Anatomical Technology, § 962. 
