CIRCULATORY SYSTEM OF ELASMOBRANCHS. 443 
branches. Each commences by the side of the lobi inferiores just 
behind the optic chiasma and passes backwards, draining the 
saccus vasculosus, to unite behind the pituitary body to form a 
median vessel. This runs the length of the spinal cord, giving 
off small segmental branches. 
3.iv. The Nutrient Branchial Veins (Parker) are a series of 
four indistinct vessels on each side which bring back the 
blood from the four holobranchs. Their anatomical relations 
do not appear to be so constant and cannot be made out so 
definitely as in Mustelus. 
4. The Inferior Jugular Sinus (Parker) [Pls. I. & IL, I.J.] is 
a moderate-sized, indefinite vessel situated below the floor of the 
mouth. It commences as a small vein shortly behind the 
symphysis of the lower jaw and passes backwards to the level of 
the hinder end of the thyroid gland, where it receives the hyoidean 
sinus and also anastomoses with its fellow. This anterier seg- 
ment may perhaps correspond with the mandibular vein described 
by Parker. The anastomosis between the two inferior jugulars 
takes the form of an extremely irregular trunk passing along the 
base of the thyroid gland (around which blood-clots are fr equently 
to be found) and irowlniene the innominate arteries. From this 
point the jugular sinus widens out considerably and runs along 
the internal sides of the ventral ends of the gill-clefts, bathing the 
proximal parts of the afferent branchial arteries, back to the wall 
of the pericardium. Here it narrows and passes along the 
wall to open into the proximal part of the ductus Cuvieri by an 
opening common to it and the sub-clavian vein. 
LV. THe Post-CAarDINAL VESSELS. 
The Posterior Cardinal Sinus. 
1. The Renal Veins. 
2. The Genital Sinus. 
A. The Ovarian Sinus. 
B. The Spermatic Vein. 
2. i. The Intestino-Mesenteric Vein. 
. The Anterior Parietal Veins. 
The Anterior Oviducal Sinus. 
The Sub-scapular Sinus. 
SR se 
The Spinal and Hsophageal Veins. 
The Posterior Cardinal Sinus (Parker) [Pls. I. & U., P.Ca.] 
originates between the kidneys, where the two posterior comaline) 
sinuses are united to form a median vessel. At the anterior end 
of the kidneys the right and left sinuses are usually separated by 
a partition passing frem the dorsal to the ventral wall in the 
