THE VASCULAR NETWORKS (RETIA 



MIRABILIA) OF THE FIN WHALE 



(BALAENOPTERA PHY S ALUS) 



By F. D. Ommanney, A.R.C.S., B.Sc. 



(Text-figs, i-io) 



INTRODUCTION 



Vascular networks lining the thorax of Cetacea were mentioned by Hunter (1787, 

 pp. 371-450) who wrote of them as follows: "The general structure of the arteries 

 resembles that of other mammals and where parts are nearly similar their distribution 

 is likewise similar. The aorta forms its usual curve and sends off the carotid and sub- 

 clavian arteries. Animals of this tribe, as has been observed, have a greater proportion 

 of blood than any other known and there are many arteries apparently intended as 

 reservoirs where a large quantity of arterial blood seemed to be required in a part and 

 vascularity could not be the only object. Thus we find the intercostal arteries divide 

 into a great number of branches in a serpentine course between the pleural ribs and 

 their muscles — making a thick substance similar to that formed by the spermatic artery 

 in the bull". 



"These vessels, everywhere lining the sides of the thorax, pass in between the ribs 

 near their articulation and also behind the ligamentous attachments of the ribs and 

 anastomose with each other. The medulla spinalis is surrounded with a network of 

 arteries in the same manner, more especially where it comes out from the brain, where 

 a thick substance is formed by their ramifications and convolutions, and these vessels 

 most probably anastomose with those of the thorax." 



Since Hunter's time these vascular networks have been noticed by many anatomists. 



Breschet (1836) described at some length a mass of vessels in the thorax of Delphinus 

 (= Phocaena) phocaena. " II existe sur l'un et l'autre cote de la colonne rachidienne 

 au-devant des cotes, derriere les plevres, depuis le sommet jusqu'a la base de la poitrine, 

 au-dessus du diaphragme, un vaste plexus vasculaire, auquel nous devons, d'apres sa 

 disposition, reconnaitre trois faces, trois bords et trois extremites." Breschet noticed 

 that intercostal nerves, sympathetic branches and ganglia were in connection with the 

 plexus. This author states definitely that the plexus is arterial in constitution. "In all 

 the intrathoracic part of the plexus veins are not discernible except as rare and small 

 branches." He continues: "From the posterior part of the plexus a number of pro- 

 longations penetrate to the neural canal and form a plexus on the posterior part of the 

 spinal ' marrow ' comparable to the spinal plexus in man — except that in man the plexus 

 is essentially formed by veins while in whales it is almost all artery". 



