CIRCULATORY SYSTEM 



53 



But the whole matter was described at considerable length 

 by Gabrod, who had more abundant material to work upon, 

 but who, nevertheless, left for his successor Forbes one out 

 of the eight known types to describe. The most prevalent 

 type is that illustrated in fig. 32. It characterises a large 

 number of birds. The two carotids are of equal size, and 

 run up the neck for the latter part of their course in the 

 hypapophysial canal. A modification of this (fig. 33) is seen 

 in the common bittern and other birds, where the carotids 

 are of equal size, but fuse into one trunk early in their 

 course. In Phoenicopterus the right (fig. 34) and in Cacatua 



Fig. 36. — Cakotids of Passeeine. 

 Lbtteeing as in Fig. 32. 



Fig. 37. — Abnormal Aeeangement 

 OF Caeotids, wheee the Left is 

 Sdpeeficiai; in Position. 



sulpliurea (fig. 35) the left of the two trunks, which are later 

 fused together, are very much the smaller. This state of 

 affairs leads to the condition shown in Passeres, where the 

 left carotid alone is present (fig. 36). Quite exceptionally, 

 and only seen in two species of the bustard, genus Eupodotis, 

 the right carotid alone is present. 



A very curious modification of the carotids is seen (ex- 

 ceptionally, according to Fubbringeb) in the hornbill, 

 Bucorvus. Here the two carotids are entirely superficial, 

 running up the neck in company with the vagus nerves. In 

 this case, as Ottley discovered, the true carotids are reduced 

 to the condition of white imperforate cords, the developed 



