164 



WHALES 



Rch 



Figure g§. Top : The main veins and their retia in a porpoise. ( The cervical and thoracic 

 retia are not shown.) J = jugular vein; Rb = brachial rele ; Re = basi-cranial rele ; 

 Aha = anterior vena cava; H = hepatic vein; P = portal vein; S ~ spinal vein; Rp = 

 pelvic rete ; Rch = chevron-canal rete; Vc = superficial caudal vein. {Slijper, igsG.) 

 Bottom : The main arteries and some retia in a porpoise. ( The cervical and thoracic retia are 

 not shown.) Re = cranial rete ; C = partially closed internal carotid artery ; Rb = brachial 

 rete ; Rs = spinal rete crossed by two arteries carrying blood to the brain cavity ; Ao = aorta; 

 Rch = chevron canal rete. {Slijper, igsG.) 



myself found that in Little Piked Whales the networks, at least in the 

 anterior thorax, spread out fairly wide in a lateral direction. 



Mixed networks containing arteries and veins are, moreover, found in 

 other parts of the Cetacean body as well (Fig. 95). We have already 

 mentioned their presence in the chevron canal, where, by the way, they 

 are only found in Odontocetes and in Little Piked Whales. In big Rorquals, 

 which have only one large artery and one large vein in the chevron canal, 

 the retia are particularly well devek^ped in the neural canal, i.e. the space 

 in the neural arch in which the spinal cord is also situated. The neural 

 retia are joined to the thoracic retia, and continue into the cranium where, 

 in all Cetaceans, they join a particularly well-developed basi-cranial 

 network in the vicinity of the hypophysis. From here the retia continue 

 along the optic nerve, and together with the arteries which, in Odonto- 

 cetes, lie embedded in it, they supply most of the brain's blood require- 

 ments, since, in Cetaceans, the internal carotid artery has a very narrow 

 lumen. These retia act as a shock-absorber against the effects of the inter- 

 mittent spurts of blood to the brain. All Cetaceans also have a particularly 



