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PROFESSOR T. J. PARKER OK THE 
B. System of the cardinal veins. 
5. The precaval sinus. 
Described and figured, but not named, by Monro (16). 
Truncus transversus, Ductus Cuvieri, Stannius (25). 
Canal de Cuvier, Milne Edwards (14). 
Precavad vein, Owen (19). 
Ductus Cuvieri, Huxley (10), Bolleston (24), Gegenbaur (7). 
Cuvierian duct, Macalister (13). 
Precaval sinus, Parker (21 and 23). 
The paired precaval sinuses are tlie homologues of the great precaval veins or 
Cuvierian ducts of Teleosts and of the precaval veins or venae cavae anteriores 
s. superiores of the higher Vertebrata. Owing to their form the name of sinus 
is more applicable to them than that of vein in Elasmobranchs. 
The precaval sinus of Mustelus (Plate 34, figs. 1 and 2 ; Plate 35. figs. 9 and 10 ; 
Plate 37, figs. 19, 27, and 28, Pr. cav. S .) is a tubular chamber, about 15 mms. 
long and 5 mms. wide, situated immediately laterad of (external to) the sinus 
venosus, of which, on anatomical grounds alone, it might be looked upon as merely 
an extra-pericardial portion. From its junction with the sinus venosus it takes a 
direction upwards and outwards (fig. 19), its antero-lateral wall lying in close appo¬ 
sition to the fifth branchial arch (fig. 10) at the junction of the epi- and cerato- 
branchial, while its inner wall is closely applied to the oesophagus. Its precise relations 
are best seen in transverse and horizontal sections of frozen specimens (figs. 9 and 19), 
in which also the apertures of the various veins into the sinus are well displayed. 
There is no constriction between the precaval sinus and the sinus venosus, the 
boundary between the two being marked only by a very low inconspicuous ridge 
in the lining membrane and by the position of the pericardial wall. Dorsally the 
precaval sinus passes with but slight change of diameter into the jugular vein, 
the entrance of which (figs. 2, 9, and 19, Jug. V'.) is guarded by a pair of semilunar 
valves ; these act so perfectly that I have never known even a drop of injection 
to pass from the sinus into the vein. In the posterior wall of the precaval sinus 
is the large valveless aperture of the cardinal sinus {Card. S'.) ; on its ventral wall, 
close to its junction with the sinus venosus is a small aperture communicating with 
the lateral vein {Lat. V'.), and, lastly, in its antero-ventral region in the somewhat 
larger opening of the inferior jugular vein {Inf. Jug. V'.). 
