Rete Mirabile Ophthalmicum 



and Intercarotid Anastomosis in Procellariiformes 



Taken off the North Carolina Coast 



Gilbert S. Grant 1 



North Carolina State Museum of Natural History, 

 P.O. Box 27647, Raleigh, North Carolina 27611 



ABSTRACT. — Dissections of arterial circulation patterns were made 

 in eleven species of procellariiform birds taken off the coast of North 

 Carolina. All species possessed well-developed rete mirabile ophthal- 

 micums (RMO) and intercarotid anastomoses, both playing a role in 

 selectively shunting blood flow and counter-current heat exchange to 

 facilitate thermoregulation and maintaining brain temperatures lower 

 than body temperatures during heat stress. There was no correlation 

 between relative size of the RMO and nesting latitude, but RMO size 

 was relatively greater in the smaller members of the order. 



INTRODUCTION 



Kilgore et al. (1979) and Bernstein et al. (1979a, 1979b) showed that 

 the presence of a rete mirabile ophthalmicum (RMO) was associated 

 with a reduction in brain temperature in heat stressed birds. The rete 

 facilitates counter-current heat exchange between the arterial blood 

 supply to the brain and the venous blood draining the evaporative sur- 

 faces of the mouth and the cornea. RMO's have been reported in a 

 number of species (Richards and Sykes 1967; Lucas 1970; Kilgore et al. 

 1976; Crowe and Crowe 1979; Pettit et al. 1981). Pettit et al. (1981) 

 examined the anatomy of the RMO of Hawaiian seabirds that may 

 encounter stressful thermal environments at their tropical nesting sites. 

 An additional site for possible counter-current heat exchange lies in the 

 cavernous sinus that houses the carotid vein and the intercarotid anas- 

 tomosis (Baumel and Gerchman 1968). These authors described three 

 major types of intercarotid anastomoses in birds. 



My study was undertaken to determine if the RMO and the type of 

 intercarotid anastomosis in procellariiform birds breeding near the 

 poles, in the temperate zones, and in the tropics differed, perhaps in 

 response to thermal stresses encountered at the nesting colony. One 

 might predict that tropical, open, ground-nesting species are exposed to 

 greater thermal stress and therefore would have relatively larger retes. 



METHODS 



Most specimens were collected 30 to 60 km off the North Carolina 



'Present address: Route 2, Box 431, Sneads Ferry, North Carolina 28460 



Brimleyana No. 11:81-86, October 1985 8 1 



