VEINS OF BIRDS. 



203 



in the frequent anastomoses, which exist more especially amongst 

 the arteries of the head and tlie viscera. Similar communications 

 occur between the veins.' ' 



Besides the remarkable arterial plexuses mentioned in the 

 general description, as the orbital, the temporal, the spermatic 

 plexuses, &c., that which Bar- 

 kow^ has described under the 

 name of the plexus of the 

 organ of incubation (^Brutor- 

 gane) deserves special notice. 

 It is represented at 17, 18, fig. 

 93, and is composed of branches 

 coming from the posterior tho- 

 racic, abdominal, cutaneous, 

 and ischiadic arteries, which 

 ramify beneath the integument 

 of the abdomen, and form, by 

 their unions, a rich network 

 of vessels which becomes truly 

 extraordinary in the time of 

 hatching. At this period many 

 birds pluck off the feathers 

 from the seat of incubation, 

 probably thereto impelled by 

 the o-reat deo-ree of heat caused 

 by the influx of blood into the 

 incubating plexus. 



§ 155. Veins of Birds. — 

 The venous blood is returned 

 to the heart by means of three 

 trunks ; two of these are j^re- 

 cavals, fig. 90, «, h, and one 

 postcaval, ib. c. Each preca- 

 val, fig. 94, a, is composed of 

 the jugular and vertebral, and 

 the veins of the wing. 



* The vertebral vein is lodged in the same canal with the verte- 

 bral artery ; it anastomoses between the vertebras with the veins 

 of the my clonal membranes. It also freely communicates at the 

 base of the cranium with the jugular vein, and receives blood 

 from the muscles of the neck. 



' The jugular vein, fig. 94, b, is a single trunk in birds, and 



Veins of a Fowl. 



