A HUMAN EMBRYO OF TWENTY-FOUR PAIRS OF SOMITES. 153 



preted to be the vena cerebri posterior. Just caudal to this vein is a longer 

 vein, which, arising in the region of the first segment and extending anteriorly 

 and ventrally, joins the anterior cardinal vein at the point where the latter is 

 broken up into two portions. I am in doubt concerning its identity. Several 

 small dorsal tributaries of varying size are received throughout the remainder of 

 the vena cardinalis anterior. They include the lateral loops of the second, third, 

 and fourth dorsal segmented arteries, which are described below. 



The ventral tributaries are more numerous than the dorsal. They may be 

 described as belonging to the different visceral arches. One arises in the man- 

 dibular arch close to the mouth, passes dorsalwards, and unites with a network 

 of small veins. The blood from this tributary may reach the anterior cardinal 

 vein, either in the region of the trigeminal or of the acustico-facial ganglion. 



The venous tributaries of the second arch do not arise as far down as those 

 of the mandibular arch. They form a plexus which lies in close relation to the 

 facial nerve. One tributary passes medially to the ganglion, while the others are 

 laterally situated. There is thus established about the acustico-facial ganglion a 

 venous ring. The plexus anastomoses with that of the first arch. 



In the upper part of the third arch are found three small tributaries, which 

 unite and reach the anterior cardinal vein as a single vessel. No others are found 

 in this visceral arch. Farther caudally, opposite the second and third somites, 

 several small veins unite with the anterior cardinal. They probably represent 

 similar tributaries from the fourth arch. 



At the point at which the anterior cardinal veins empty into the common 

 cardinal there is received, on the ventral side, a long, slender vein (vena linguo- 

 facialis). The smallest tributaries of this vein may be traced as far as the third 

 visceral arch. Uniting, these tributaries form the vein which proceeds caudally 

 and dorsally. In its course it passes in the antero-lateral body-wall over the 

 heart. A similar vein has been described by Ingalls 19 , as follows: 



"Am Anfang des Ductus Cuvieri miinden in ihn auf jeder Seite je ein von der vor- 

 deren Bauchwand kommendes Gefass. Auf der rechten Seite 1st dies besonders gross, 

 es liisst sich ventralwiirts bis in die Niihe des Ursprungs der ersten Aortenbogen verfolgen 

 and weiter Kaudalwiirts bis dahin, wo die ersten Kiemenbogen mit der vorderen Korper- 

 wand verschmolzen sind, vim sich schliesslich in dem ersten Bogen zu verlieren." 



The same vein had been found by Salzer 40 in embryos of the guinea-pig and 

 later by Grosser 16 in bat embryos. Lewis 26 describes it in the pig embryo under 

 the term "transverse vein," and later 27 discussed its origin and fate in rabbit and 

 human embryos. Apparently the first reference to this vein, which is now 

 recognized as of constant occurrence and fundamental morphological importance, 

 was made by Phisalix, as Dr. Lewis has pointed out to me. Phisalix 39 , in 1888, 

 showed it clearly in a figure of a 10 mm. human embryo and described it as follows: 



"Entre la veine jugulaire et la veine cardinale se trouve une vasto poche dont le sang 

 s'ecoule par les canaux de Cuvier .... En avant et au-dessus, chacune de ces poches 

 regoit des veinules qui accompagnent le nerf hypoglosse et qui vioimont do la base des 

 arcs branchiaux." 



