A Comparative Account of the Vascular System of Certain Rajiform Fishes.
[Read before the Otago Branch, July 11, 1944; received by the Editor, August 14, 1944, issued separately, March, 1945.]
Having investigated Squatina squatina, one of us (B. J. M.) began, in England, to study the vascular system in various species of Raja. In New Zealand a start was made also on the dissection of the highly specialised Blind Numb Fish Typhlonarke aysoni, and the work was then taken over by M. L. P., who is responsible for the drawings and descriptions in this paper, and most of the dissections upon which they are based. The species of ray whose vascular system has been most fully described is R. nasuta, studied by T. J. Parker in this department towards the end of last century. Dissections were made of this species as a typical ray, and single specimens of the Stingray, Bathytoshia brevicaudata, and the Electric Ray Notastrape fairchildi were also dissected. The names used here are those given by Whitley (1940). Among the specimens of Typhlonarke dissected, some appeared to differ externally from T. aysoni and probably belong to another species, but no differences in the vascular system were observed.
The order Selachii is divided by Goodrich (1930) as follows: Grou p 1. Notidani.
|Group 2. A. Suborder Heterodonti.|
|B. (a) Suborder Scylloidei.|
|(b) Suborder Squaliformes.|
|(c) Suborder Rajiformes.|
|Sec. 1. Squatinoidei.|
|Sec. 2. Rhinoraji.|
|Sec. 3. Centrobatoidei.|
|Sec. 4. Torpedinoidei.|
Detailed studies of Selachian vascular systems are not very numerous, but members of the Notidani have been described by Daniel (1928), of the Scylloidei by Parker (1886), O'Donoghue (1914), and Marples (1936, 1), and of the Squaliformes by O'Donoghue (1928). Marples (1936, 2) described the vascular system of Squatina and gave reasons for its removal from the Rajiformes. No complete description of members of the Rajiform groups appears to exist, the most complete being that of R. nasuta by Parker (1884), while the posterior region of R. erinacea was described by Rand and Ulrich (1905) and Daniel (1928) gave certain details of Dasyatis dipterura, a stingray belonging to the Centrobatoidei. The present paper is an attempt to add to our knowledge of the vascular system of the Rajiformes, but a great deal of interesting work remains to be done when material is available, especially among
the stingrays. It may be mentioned that Goodrich (1909) suggests a connection between the Rhinobatidae, Pristidae and Rajidae, but a separate origin from the primitive Rajiform stock for the Torpedinidae, Trygonidae and Myliobatidae, with the Torpedinidae nearest to the Rajidae.
Typhlonarke has such a peculiarly modified skeleton that a brief description is desirable and the general disposition of the parts is shown in Fig. 1. It is oval in shape, with a very abbreviated tail and small mouth. The pectoral fins arise very far back and the pectoral and pelvic girdles overlap considerably. Between the pectoral fins and the anterior part of the body lie the large electric organs. Goodrich (1909) states that in the Torpedinidae the two halves of the pectoral girdle are not firmly fused together, but this is not true of Typhlonarke.
The sinns venosus is a triangular chamber into which run the ductus Cuvieri of the right and left sides. It opens into the atrium, which, is a large, thin-walled chamber. This lies dorsal to the ventricle into which it opens on the left side. The ventricle has very thick muscular walls and is asymmetrical, being rather larger on the left side than on the right. It runs forward, narrowing into the conus arteriosus. The valves of the conus have been used to a certain extent in classification. In the most primitive sharks there are three longitudinal rows of four valves. In most sharks this number is decreased, while in rays it is increased, at least this is the general supposition. But of the animals examined, R. nasuta, the stingray and Torpedo, all resemble the primitive sharks in having three long rows each containing four valves. In Typhlonarke one of the rows
contains three valves, the others four. It seems, therefore, that an increase in the number of valves is by no means universal among the rays.
The Ventral Aorta.
The ventral aorta arises from the conus arteriosus and runs forward ventrally in the midline. Normally the ventral aorta runs forward to the level of the first gill-slit before bifurcating (Fig. 3, A and C), but in Torpedo (Fig. 3, B) it is shorter and bifurcates on a level with the second gill-slit.
The Afferent Branchial Arteries.
In Typhlonarke (Fig. 3, C) almost immediately after leaving the conus, two stout branches are given off symmetrically from the ventral aorta. These redivide into two, the posterior ones being the fifth afferent arteries. At once the anterior branches redivide forming the third and fourth afferent arteries. On a level with the first gill-slit the ventral aorta bifurcates into the two innominate arteries, which divide to form the first and second afferent arteries. The afferent arteries are dorsal to the jugular sinus.
The three species of Rajidae examined, R. nasuta, R. clavata and R. batis, are all similar to Typhlonarke in the origin of their afferent arteries, while in Torpedo the common stem of the three posterior ones is quite short (Fig. 3, B). The Stingray, however, has the three posterior arteries arising separately though close together from the ventral aorta. This is figured also by Daniel (p. 178) for D. dipterura. In this respect the stingrays resemble the sharks, where the third, fourth and fifth afferent arteries never arise from the ventral aorta by a common stem, though the fourth and fifth may do so.
The Efferent Branchial Arteries. (Fig. 2.)
In Typhlonarke, as in other Selachians (Fig. 2, C) the efferent branchial arteries form complete loops around the first four gillslits. The fifth gill-slit has only an anterior hemibranch, and so an efferent artery only upon the anterior side. These loops are all connected by commissural arteries which traverse the gill-bars. From these commissural arteries arise the arteries which supply the electric organ (e.a.). The most anterior vessel to this organ (e., a.,) arises from the hyoidean epibranchial artery. From the ventral ends of the efferent loops arise the hypobranchial arteries (Fig. 3, C), while from their dorsal ends the epibranchial arteries (ef.a.) originate.
This arrangement is common to all the fishes examined, except for the arteries to the electric organ, which are possessed by Typhlonarke and Torpedo only.
The Dorsal Aorta. (Fig. 2.)
The dorsal aorta runs along the median axis of the body, dorsal to the gut and ventral to the spinal column. Its anterior end, the paired internal carotid arteries, pierces the brain case, while its posterior part supplies the tail as the caudal artery, which lies in the haemal canal of the caudal vertebrae.
In sharks, there are anteriorly two lateral dorsal aortae, which receive the hyoidean epibranchial arteries and unite to form the internal carotid artery. In none of the fishes examined were there any signs of the lateral dorsal aortae extending forward to join
the hyoidean epibranchial arteries as in sharks, though the common bases of the first and second epibranchial arteries of Raja and
Typhlonarke on each side (Fig. 2, B and C) are presumably lateral dorsal aortae. Absence or interruption of the lateral dorsal aortae seems characteristic of the rays, while these vessels are complete in the sharks (Daniel) and in Sqnatina (Marples).
In Typhlonarke (Fig. 2, C) the dorsal aorta bifurcates anteriorly into the common stems of the first and second epibranchial arteries. The third and fourth enter the dorsal aorta separately. Just posterior to the fourth epibranchial arteries the coeliac artery (c), then the subclavians (scl.a.) and then the anterior mesenteric (a.m.) arteries are given off. The posterior mesenteric (p.m.) and iliac arteries (i.a.) are given off much further back.
In the stingray (Fig. 2, A) the four epibranchial arteries enter the dorsal aorta separately, and the subclavian arteries arise posterior to the third epibranchial and anterior to the fourth. The coeliac and anterior mesenteric arteries arise posterior to the fourth epibranchial artery. In R. nasuta (Fig. 2, B) the first and second epibranchial arteries have a common stem as in Typhlonarke, but the subclavian arteries arise posterior to this common stem, and anterior to the third epibranchial arteries. Typhlonarkeis peculiar in that the subclavian arteries arise very far back, not only posterior to the last epibranchial but to the coeliac artery as well. This may be correlated with the abnormally posterior position of the base of the pectoral fins.
In Typhlonarke, Torpedo and the Rajidae, the first and second epibranchial arteries enter the dorsal aorta by a common stem. This condition is not found in sharks, which in this respect are like the stingrays. In these, the first three epibranchial arteries enter the dorsal aorta very close together, the fourth much further back.
In Typhlonarke, close to the efferent loops, a branch, (s.a.) is given off from each epibranchial artery to supply the dorsal superficial musculature of the pharynx and the gill flaps. Similar arteries were found in the Stingray accompanying the cutaneous veins (Fig. 4, A, c.v.) which empty into the anterior cardinal sinus. In R. nasuta only one superficial artery is present, arising from the third epibranchial artery and giving an anterior, and a posterior branch supplying the superficial musculature.
Arteries of the Head. (Fig. 2.) 1
In Typhlonarke the hyoidean epibranchial artery (h.) arises from the first efferent branchial loop and passes forward to join its fellow from the opposite side and enter the brain case as the internal carotid artery. Just after leaving the efferent loop it gives rise to a superficial artery (s.a.). This artery divides into three branches, one of which goes to the superficial spiracular region, another to the muscles about the otic capsule, and the third to the dorsal surfaces of the lateral rostral cartilages. Just anterior to the superficial artery another branch arises (e., a.,) which runs to the electric organ. This artery is not similar morphologically to the other arteries supplying, the electric organ, for if it were it would arise from the afferent spiracular artery, (a.s.a.) which corresponds to the commissural arteries between the efferent loops. Nor, is it homologous with the orbital artery, which passes anterior to the spiracle, while this artery
is behind it. The orbital artery is absent in Typhlonarke. This fish is blind, and the eyes are reduced to small remnants, but as the orbital artery usually supplies a considerable part of the anterior region of the head as well as the eye muscles, this would not seem to account for its absence. In Torpedo, R. nasuta and the Stingray, the hyoidean epibranchial artery gives rise to an orbital artery (o.a.) which passes ventral to the brain case, and in the orbit runs dorsal to the efferent spiracular artery (e.s.a.) but ventral to nerves V and VII, to which it runs parallel. In front of the eye it divides into two, the median branch supplying the ventral surface of the rostral cartilages and giving a branch to the roof of the mouth, the lateral one turning posteriorly to supply the muscles of the upper jaw.
After the orbital artery has been given off, the two vessels, now usually known as the internal carotid arteries and representing morphologically the anterior ends of the lateral dorsal aortae, proceed anteriorly and unite in the middle line to pass through a foramen on the floor of the brain case. Inside, a branch is given dorsally which divides into anterior and posterior cerebral arteries. The posterior cerebral arteries pass along the posterior region of the brain to the spinal cord and are there augmented by branches of the segmental arteries.
Spiracular Arteries. (Fig. 2.)
These are often called the pseudobranchial arteries, but, as a pseudobranch is not always present, spiracular is perhaps the better term. In Typhlonarke the afferent spiracular artery (a.s.a.) passes median to the pseudohyal and lateral to the hyomandibular cartilage. Before reaching the spiracle, it gives off a branch (a.m.a.) which possibly represents the afferent mandibular artery, the mandibular arterial arch being interrupted in its lower half in all elasmobranchs except Squatina squatina and Callorhynchus antarcticus. This branch is also present in Torpedo and Raja, but as in Typhlonarke, there is no ventral connection. The efferent spiracular artery (e.s.a) is in Typhlonarke a very fine vessel which leaves the spiracle, passes through the cartilage of the brain case, and joins the internal carotid artery, having given off the ophthalmic artery (oph.a.) before passing through the cartilage. This artery gives a branch to supply the muscles of the lower jaw and proceeds forward to supply the rostral cartilages.
In R. nasuta (Fig. 2, B) the afferent spiracular artery proceeds on the median side of the pseudohyal cartilage, lateral to the hyomandibular, and gives off the afferent mandibular artery before reaching the spiracle. From here the efferent spiracular artery passes across the floor of the orbit, ventral to the orbital artery. Median to it, it gives off the ophthalmic artery which runs along the mediodorsal surface of nerves V and VII, and supplies the eye.
The hypobranchial arteries arise from the ventral ends of the efferent loops and form a complicated system of vessels on the ventral wall of the pharynx. They supply the heart by the coronary arteries, and are joined to the subclavian arteries (s.cl.a.) by the coracoid arteries (cor.a.). In Typhlonarke the first hypobranchial artery arises from the first efferent loop and runs medio-posteriorly, ventral to the afferent arteries. It divides into two arteries, both supplying the thyroid gland. The second, third and even the fourth hypobranchial arteries may unite and run backwards as the lateral hypobranchial artery (l.h., Figs. 3 and 5). The second does not always join the lateral hypobranchial. The first gives rise to a superficial artery (Fig. 5, s.h. 1) laterally which divides to supply the ventral musculature of the gill flaps and the pharynx. A similar one arises from the second hypobranchial (s.h. 2), but the third superficial artery (s.h. 3) arises, not from the third hypobranchial but from the lateral hypobranchial. It supplies the last three gill flaps. The coronary artery (Fig. 3, C, cn.a.) arises from the median side of the lateral hypobranchial and runs along the common stem of the three posterior afferent arteries. On the left side, the coronary artery, before reaching the ventral aorta gives off a dorsal pericardial branch (d.p.). On the ventral aorta it turns posteriorly at right angles and runs along the conus to the ventricle. On this it divides into a ventral coronary artery (v.c.a.) and a dorsal coronary artery (d.c.a.). The lateral hypobranchial artery gives a branch to the ventral wall of the pericardium, but there is no posterior coronary artery. The lateral hypobranchial continues backwards as the coracoid artery (cor., Figs. 3 and 5), which passes dorsal to the coracoid cartilage and joins the subclavian artery.
In Torpedo (Fig. 3, B) as in Typhlonarke the first hypobranchial is not connected to the second, but it is the second which supplies the thyroid gland. The second hypobranchial runs towards the ventral aorta, sends two branches anteriorly, and then is joined to the third hypobranchial by a commissural vessel (c.h.a.). This was found on one side only. The coronaries arise one from the commissural hypobranchial and the other from the base of a sqxiare formed by the arteries on the ventral aorta. The third hypobranchial sweeps back as the coracoid artery dorsal to the coracoid cartilage. Owing to the posterior part of the specimen being destroyed it was not possible to locate a connection with the subclavian artery, though one no doubt exists.
In Typhlonarke the lateral hypobranchial artery is ventral to the afferent arteries. This is not the case in the sharks, where this vessel is dorsal to the afferent arteries and median hypobranchials are
present ventral to the afferent system, as in M. antarcticus, M. canis, and S. squatina. In Hexanchus corinus the median hypobranchial arteries are dorsal to the afferent arteries but the coracoid arteries have a common median stem on the ventral side of the ventral aorta (Daniel, pp. 164 and 178). It seems possible that the ventrally situated, so-called “lateral hypobranchial arteries” of Raja and the median hypobranchial arteries more or less fused on the ventral side of the ventral aorta of Mustelus, are homologous vessels. The median hypobranchial arteries of Dasyatis and Squatina are more or less intermediate in position. The coracoid arteries always arise from the ventral vessel whether medially or laterally situated. Of course it it always possible that commissural vessels of the hypobranehial system were formed surrounding an afferent artery and then that, the dorsal portion was lost. This would account for the condition found in R. nasuta and R. clavata. In these the lateral hypobranchial artery connects up the hypobranchials of the first four gill slits. It runs dorsal to the second afferent artery and ventral to the others. The superficial musculature is supplied by a branch arising from the lateral hypobranchial about the level of the third gill slit. Daniel (p. 178) states that the lateral hypobranchial is incomplete in R. clavata, so there appears to be variation in this arrangement.
Paired Arteries. (Fig. 2.)
In Typhlonarke the subclavian arteries arise symmetrically posterior to the fourth epibranchial arteries. An ovarian branch (ov.) is given off, running posteriorly, parallel to the dorsal aorta, then another branch runs to the dorsal musculature (d.m.). The coracoid artery (cor.) joins the subclavian artery after passing dorsal to the coracoid cartilage and arising from the hypobranehial system as described above. In Typhionarke the coracoid artery is very fine in comparison with the wide vessel in R. nasuta. In R. nasuta the subelavian artery receives the coracoid artery at a point just median and ventral to the division into the propterygial and metapterygial arteries. From the propterygial artery about two centimeters from where the subclavian divides, a branch passes round dorsally to the anterior side of the propterygial cartilage. A ventral abdominal branch (Fig. 2, B, v.a.a.) from the metapterygial artery runs medioposteriorly on the dorsal side of the metapterygial cartilage along the ventral body wall to join the iliac artery. From the subclavian there arises the lateral abdominal artery (l.a.a.), which passes along the side of the body cavity and joins the femoral artery lateral to the ventral abdominal artery.
In Typhlonarke the iliac arteries have cloacal arteries arising from them, of which the right one is the larger. A dorsal artery (d.m.) supplies the dorsal muscles, and the iliac artery then supplies the fin. A branch of fair size is given to the anterior basal cartilage and also supplies the first few radials. The remainder of the radials are supplied by an artery which proceeds backwards, dorsal to the radials and lateral to the basipterygium.
In R. nasuta (Fig. 2, B) two spermatic arteries arise median to the cloacal arteries and pass anteriorly. After receiving the ventral abdominal and then the lateral abdominal arteries, the iliac artery divides in the fin. In R. montagui a branch from near the base of
the iliac artery runs forward along the median side of the kidney, sends a branch to the posterior fused portion of the oviducts and anastomoses with two large segmental arteries which leave the dorsal aorta near the anterior end of the kidney. The oyiducal gland and anterior part of the oviducts are supplied by branches of three large segmental arteries arising anterior to the kidneys.
The Anterior Cardinal Sinus. (Fig. 4.)
In Typhlonarke (Fig. 4, C) the anterior cardinal sinus (a.c.s.) stretches from the back of the auditory capsule to the end of the ductus Cuvieri (d.c.). Anteriorly it receives the hyoidean sinus (h.s.), which connects it to the jugular sinus (j.s.), the post-orbital sinus (p.o.s.) and the posterior cerebral vein (p.c.v.). Along its length a vein is received from each gill-bar, which, like the hyoidean vein, extend from the anterior cardinal to the jugular. All these receive veins from the electric organ (e.v., Fig. 5). Cutaneous veins draining the gill pouches also enter the anterior cardinal. The post-orbital sinus is a narrow vessel running lateral to the auditory capsule, ventral to an overhanging ledge of cartilage, and connecting the anterior cardinal to the orbital sinus. The posterior cerebral vein passes through the cranium with the vagus and the vein on the right is larger than the one on the left. Each vein divides into two, the anterior branch on each side uniting with the one from the other side in front of the cerebellum, from which point a vein runs forward along each side of the brain and receives branches from its surface. The posterior branches of the cerebral veins join behind the cerebellum and pass back along the spinal cord as the myelonal vein.
A vein which drains the jaw muscles enters the post-orbital sinus. The orbital sinus receives laterally a vein which branches about the spiracle and another supplying the eye. The interorbital sinus (i.o.s.) which is very well formed, leaves the orbital sinus just posterior to the articulation of the rostral cartilages with the brain case. It runs for about half an inch on the antero-lateral inside wall of the brain case before passing ventrally through the cartilage to the under surface, where it unites with the interorbital sinus of the opposite side. Ventral to the brain ease branches are received from the olfactory organ. This condition is very different from that described by O'Donaghue for Scyllium canicula in which “the interorbital vein is a small but well marked vein running from one orbit to the other in a canal in the basicranial cartilage, and it enters the orbit toward its posterior end just in front of and slightly below the large foramen in the cranium through which the sixth and main branches of the fifth and seventh nerves leave the cranium.” In Typhlonarke it is much further forward, and for a part of its length runs on the inside of the cranium.
In the Stingray (Fig. 4, A) the anterior cardinal sinus receives anteriorly the post-orbital sinus, the posterior cerebral vein and from the gill-bars, the hyoidean and branchial veins as in Typhlonarke. Medianly four cutaneous veins (c.v.) enter the anterior cardinal sinus. Dorsally they unite into a longitudinal vessel which enters the ductus Cuvieri. The post-orbital sinus also receives a cutaneous vein quite close to the point at which a pre-spiracular vein also enters the sinus.
In R. nasuta the same general arrangement of veins entering the anterior cardinal sinus is found. At the anterior border of the orbit the anterior cerebral vein (a.c.v.) enters it medianly through a foramen in the wall of the brain case, having drained the fore brain. The orbital sinus also receives branches from the olfactory organ.
In Typhlonarke the jugular sinus lies lateral to the ventral aorta and dorsal to the hypobranchial arteries, and it is connected to the anterior cardinal sinus by the hyoidean and branchial veins. In the middle line, ventral to the bifurcation of the ventral aorta, lies the thyroid sinus (t.s.) which is connected to the jugular sinus of each side by three veins. At its anterior end the jugular sinus drains a network of veins lying over the muscles of the mouth and jaws.
In R. nasuta the jugular sinus lies ventral to the afferent arteries but, posteriorly, the lateral hypobranchial artery is dorsal to it. It was not possible in either the Stingray or R. nasuta to trace the relations of the thyroid sinus, but the thyroid sinus depicted by Ferguson for R. erinacea is somewhat similar to that of Typhlonarke.
The Posterior Cardinal System. (Fig. 4.)
In Typhlonarke the posterior cardinal sinus (p.c.s.) empties into the lateral ends of the ductus Cuvieri by the cardinal veins (c.v.). Posteriorly it gives off the posterior prolongations of the cardinal veins, and medianly it also gives off a vessel, the haemorrhoidal vein (h.r.) supplying the rectal gland.
In the Stingray the posterior cardinals were not injected but they appeared to be paired as in the sharks, instead of fused into a large median sinus as in the rays.
In R. nasuta the posterior cardinal veins join to form the posterior cardinal sinus, as described by Parker. Two cardinal veins run posteriorly to the medial surfaces of the kidneys and then join. Parker gives a description of the connections of the veins of the posterior region and describes the haemorroidal vessel as joined to the lateral abdominal veins by large ileo-haemorroidal veins which passed on either side of the rectal gland. Rand and Ulrich did not find these in R. erinacea, but described a system of small anastomosing vessels connecting the haemorroidal and lateral abdominal veins. In the specimens of R. nasuta examined the arrangement agreed rather with Rand and Ulrich's description than with that of Parker for R. nasuta itself (Fig. 4, B). Ileo-haemorroidal veins similar to though smaller than those figured by Parker were found in a specimen of R. naevus.
In Typhlonarke (Figs. 4 and 5) the pectoral girdle is much modified and the lateral portions are drawn out to form a canal in which certain vessels run, and this has various openings to allow the vessels to pass out and supply the fin. From the fin, the first brachial vein (1.br.) enters an anterior fontanelle (Fig. 5), passes inside the canal, crosses to the median side of the subclavian artery, and finally enters the ductus Cuvieri dorsally. The second brachial
Figure 5.—A dissection of Typhlonarke from the ventral surface, showing the main arteries and veins. The ventral pharyngeal musculature, the pericardial wall and part of the abdominal muscles are removed and the dissection is deeper on the right side of the animal than on the left. (For explanation of letters see end of paper.)
vein (2.br.) enters the canal by a posterio-dorsal fontanelle, passes out by a medio-ventral opening and joins the lateral abdominal vein to form the subclavian vein.
In the Stingray (Fig. 4, A) the pectoral fin is supplied by three veins. The first (1.br.) drains directly into the ductus Cuvieri. This vessel passes between the propterygium and mesopterygium and divides into two, the propterygial branch running median to the artery. The second (2.br.) and third (3.br.) brachial veins join the lateral abdominal vein to form the subclavian vein, which enters the ductus Cuvieri laterally. The second vessel passes between the mesopterygium and metapterygium, and the third passes dorsal to the metapterygium.
In R. nasuta (Fig. 4, B) two veins enter the lateral abdominal vein, the anterior one (g.v.) running anterior to the propterygium and draining the gill pouches. The posterior one is the brachial vein which divides into a propterygial and a metapterygial branch to supply the fin. A transverse vessel joins the metapterygial branch to the lateral abdominal vein.
The Lateral Abdominal Vein.
The lateral abdominal vein in Typhlonarke is very short indeed, as the bases of the two paired fins are almost at the same level. It is a small stout vein running from the point where it joins the brachial vein towards the mid line, receiving the femoral vein and many small branches from the body wall. It does not join with its fellows of the opposite side. In the Stingray the two lateral abdominal veins are connected in front of the cloaca by the pelvic vein (p.v. Fig. 4, A). In this it resembles the sharks and differs from the rays in which the lateral abdominal veins arise from a number of small branches in the cloacal region. R. nasuta is typical of the rays. After giving off the femoral vein, the lateral abdominal vein forms a network upon the rectum and about the cloaca, some of the branches anastomosing with those of the haemorroidal vein as mentioned above.
The Femoral and Cloacal Veins.
In R. nasuta and the Stingray, the femoral vein and the cloacal vein join the lateral abdominal vein separately. In Typhlonarke, there is a large external basipterygial vein running lateral to the basipterygial cartilage and giving off branches between the fin radials, and several ones to the dorsal muscles. The internal basipterygial vein is short. It runs medial to the basipterygial cartilage and is joined to the external vein by commissural veins running ventral to the cartilage. In R. nasuta there is a superficial vein supplying the ventral surface of the fin, giving a branch parallel to the basipterygium and another along the front edge of the first radial. This joins the more dorsal of a pair of basipterygial veins which lie superimposed, one dorsal the other ventral to the fin radials and joined between each radial by commissural vessels. Into the ventral basipterygial vein, just before it enters the femoral vein, the pelvic transverse cutaneous vein is received. This vein leaves the lateral cutaneous trunk and passes round the back of the fin.
The cutaneous venous system was studied only in Raja, the following description being of R. batis, but the other species appeared to be essentially similar. A lateral cutaneous vein of the usual type drains the trunk on each side, and each has parallel and dorsal to it an accessory lateral cutaneous vein. These two veins join immediately behind the scapular cartilage and pass deep to it as the subscapular vein to enter the ductus Cuvieri a short distance in front of the pectoral girdle. No dorsal or ventral cutaneous veins were observed. The extreme size of the fins and their extension forward alongside the head, result in a somewhat different arrangement of the veins in this region as compared with those of Scyliorhinus and Squatina (Marples, 1936, 1, p. 324 and 1936, 2, p. 836). In these species the dorsal pectoral cutaneous vein enters the subscapular sinus posteriorly to the scapular. In Raja a posterior dorsal pectoral cutaneous vein has this course, but in addition a large anterior dorsal pectoral cutaneous vein enters the subscapular sinus anteriorly to the scapular. It runs along the junction between the gill pouches and the propterygial cartilage on the dorsal side, and arises from branches on both the dorsal and ventral surfaces of the anterior region of the fin. It also receives branches from the head and from an extensive network over the gill pouches. The middle region of the fin is drained into two large veins, one of which enters the anterior dorsal pectoral cutaneous vein, opposite the second gill pouch, the other immediately in front of the scapular cartilage. The posterior end of the fin is drained by the posterior dorsal pectoral cutaneous vein. On the ventral side, branches from the anterior and middle regions of the fin collect into veins which pass dorsally between the fin and the gill pouches to enter the anterior dorsal pectoral cutaneous vein. The posterior ventral part of the fin is drained by the ventral pectoral cutaneous vein, which enters the lateral abdominal vein immediately behind the pectoral girdle. In the pelvic fin the pelvic transverse cutaneous vein connects the basipterygial veins to the lateral cutaneous vein as described in the previous section.
The general characters of the vascular system by which the rays are held to differ from the sharks are as follows:—The lateral dorsal aortae are interrupted; the first two epibranchial arteries do not enter the dorsal aorta separately; the three posterior afferent arteries leave the ventral aorta by a common stem; the lateral hypobranchial arteries are ventral to the afferent arteries; there are no median hypobranchial arteries; the anterior mesenteric artery supplies the dorsal side of the intestine only; there is no ventral intestinal artery; there is a single posterior cardinal sinus; the lateral abdominal veins are not united posteriorly by a pelvic vein but arise from small branches in the cloacal region.
This type of vascular system is found in R. nasuta, which is typical of the Rajiformes. The Torpedonidae are also very similar, with the addition of arteries and veins supplying the electric organ. Typhlonarke is one of the most highly specialised members of this family in that its eyes are rudimentary, the fins are reduced in size and the bases of the pectoral fins are very far back. It has no orbital
artery but otherwise its vascular system is essentially similar to that of Torpedo and Raja. It is interesting to find in the Stingray, however, certain shark-like features. The first two epibranchial arteries join the dorsal aorta separately, the three posterior afferent leave the ventral aorta separately, and there is a pelvic vein connecting the posterior ends of the lateral abdominal veins. Though it could not be determined for certain in the single specimen available it seemed that the posterior cardinal sinuses do not fuse into a large median sinus. It is impossible to generalise upon details of the vascular system of two species only, but it seems possible that an extensive study might produce evidence that the Centrobatoidei represent a different line in the Rajiformes as compared with the Rhinoraji and Torpedinoidei.
The vascular system of Typhlonarke, one of the Torpedonidae, is described and compared with that of Raja nasuta and the Stingray Bathytoshia brevicaudata, with notes on other Raja sp. and Notastrape, a normal member of the Torpedonidae.
Typhlonarke is blind and is highly specialised with regard to its fins.
The Stingray has several shark-like features in its vascular system but Typhlonarke and Notastrape are of the usual rajiform type.
The large ileo-haemorroidal veins described by Parker in R. nasuta were not found, but similar ones were observed in R. naevus.
Reference Letters Used in the Text Figures.
a.c.s.—anterior cardinal sinus.
a.m.—anterior mesenteric artery.
a.m.a.—afferent mandibular artery.
a.s.a.—afferent spiracular artery.
1 br and 2 br.—brachial veins.
b.v.—branchial vein. e.a.—coeliac artery.
ed.—posterior cardinal vein,
e.h.a.—commissural hypobranchial artery.
e.v.—cardinal vein opening: into ductus Cuvieri.
d.bt.—dorsal basipterygial vein.
d.c.—dorsal coronary artery.
d.m., d'.m'.—arteries to dorsal musculature.
d.p.—dorsal pericardial artery.
e.a.—branchial electric organ artery.
e'.a'.—hyoidean electric organ artery.
e.s.a.—efferent spiracular artery.
e.v.—electric organ vein.
ex.b.—exterior basipterygial vein.
g.v.—vein draining gill pouches.
h.—hyoidean epibranchial artery.
i.b.—internal basipterygial vein.
i.e.—internal carotid artery.
l.a.a.—lateral abdominal artery.
l.a.v.—lateral abdominal vein.
l.c.—lateral cutaneous vein.
l.h.—lateral hypobranchial artery.
p.c.—posterior cerebral vein.
p.c.s.—posterior cardinal sinus.
p.cor.—posterior coronary artery.
p.m.—posterior meseuteric artery.
p.o.s.—post orbital sinus.
p.t.c.v.—pelvic transverse cutaneous vein.
s'.a'.—superficial artery of hyoid arch.
s.h. 1–3.—superficial hypobranchial arteries.
v.a.a.—ventral abdominal artery.
v.bt.—ventral basipterygial vein.
v.c.—ventral coronary artery.
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