82 Gilbert S. Grant 



coast, but a few specimens of the Northern Fulmar, Fulmarus glacialis, 

 and the Sooty Shearwater, Puffinus griseus, were found dead on North 

 Carolina beaches. The lone Antarctic Petrel, Thalassoica antarctica, was 

 obtained from D. G. Ainley via D. W. Johnston in trade. All specimens 

 on which this note is based are deposited in the collection of the North 

 Carolina State Museum of Natural History. Dissections under a binocu- 

 lar microscope were in most cases performed on pickled specimens, 

 using the methodology of Pettit et al. (1981). 



RESULTS 



Two of the three types of intercarotid anastomoses were found in the 

 eleven procellariiform species examined in this study (Table 1). There 

 was no correlation of anastomosis type with latitude (as an index of 

 potential thermoregulatory stress). 



In all cases the RMO was found in the temporal region of the head, 

 between the orbital ridge and the otic process of the quadrate. The 

 RMO is derived from the external ophthalmic branch of the internal 

 carotid artery and from branches of the facial, maxillary and mandibu- 

 lar veins. To crudely assess the relative size of the rete in 1 1 species of 

 Procellariiformes ranging in weight from 34 to 774 grams, I measured 

 the surface area of the RMO using a transparent grid. This measure 

 does not take into account the relative thickness or, more importantly, 

 the actual area of contact of the arterial and venous components of the 

 rete. However, it does give a first approximation of the relative size of 

 the rete. Surface area/ body weight ratios exhibited a slight but insignifi- 

 cant (P>0.05) increase with latitude (Table 2), while an inverse correla- 

 tion (P<0.05) of body weight and RMO surface area/ weight ratio was 

 evident. Thus, the smaller procellariiforms have relatively larger RMO's. 



DISCUSSION 



A well-developed intercarotid anastomosis unites the two carotids 

 caudal to the hypophysis in most birds examined by Baumel and 

 Gerchman (1968). They found that injection of the cervical portion of 

 one carotid resulted in bilateral filling of both the intra- and extracra- 

 nial arteries via this anastomosis. The avian intercarotid anastomosis 

 may effectively substitute for the mammalian circle of Willis in main- 

 taining brain-to-body temperature differences (Baumel and Gerchman 

 1968; Kilgore et al. 1976; Pettit et al. 1981). 



As Kilgore et al. (1976) pointed out, the effectiveness of the RMO 

 heat exchange depends on the arterial-venous temperature differential, 

 on rete blood flow and velocity, and the area and closeness of arterial- 

 venous contacts within the rete. 



Several species, including Sooty and Greater Shearwaters, and Wil- 

 son's Storm-Petrel, Oceanites oceanicus, are transequatorial migrants 



