234 STRUCTURE AND CLASSIFICATION OF BIRDS 



already hinted, in many ways an aberrant form as a type. 

 The dorsal tract (see fig. 112) gradually narrows as it 

 passes down the neck, but the feathers get stronger ; it 

 bifurcates between the scapulae to form a well-defined 

 fork, which ends ultimately, having become weaker. Between 

 this fork, and not connected with the rest of the dorsal tract, 

 appears a spear-headed patch of feathers. The ' shaft ' 

 of the ' spear ' becomes stronger as it descends to end 

 abruptly at the base of the oil gland. The ventral tract 

 is narrow between the mandibles ; it is undivided upon the 

 neck. At the beginning of the breast it divides into a wide 

 outer and a narrow inner portion, the latter being more 

 strongly feathered. The two converge on each side towards 

 the cloacal aperture, but do not reunite. 



In Capriwmlgus, on the other hand, the ventral tract bifur- 

 cates in the neck, and the two ventral tracts are single, and 

 there is no such abrupt break between the two parts of the 

 dorsal tract as has been described above in Steatornis. Nor is 

 there in Antrostomus, where there is no narrowing of the pos- 

 terior part of the dorsal tract. Nyctidromus is much the same. 1 



The tongue in the goatsuckers is more or less abortive ; in 

 Podargus it is a curious tough but transparent membranous 

 organ. 



As mentioned in the definition of the group the cceca are 

 large ; but as a unique exception ^Egotheles seems to be 

 entirely without them. In all the genera the left lobe of the 

 liver is rather the smaller ; and all, save Chordeiles, have a 

 gall bladder. The intestinal measurements in inches are 

 given on the following page. 



The intestine (according to MITCHELL) is primitive and 

 owl-like, while the ctcca are dilated apically, as in owls. 



J. MURIE, ' Fragmentary Notes on the Guacharo, or Oil Bird,' Ibis (3), iii. p. 81 ; 

 L'HEKMINIEB, 'Memoire sur Je Guacharo,' Nouv. Ann. Mns. iii. 1834, p. 321, 

 and note ' Sur la Classification Methoclique clu Guacharo,' &c., Rev. Mag. Zool. 

 (2), i. p. 321 ; J. MULLEK, ' Ueber die Anatoniie des Steatornis caripensis,' M.B. 

 k. Ahad. Wiss. Berlin, 1841, p. 172, and ' Anatomische Bemerkungen iiber den 

 Guacharo,' Arch. f. Auat. it. Phys. 1842, p. 1. 



1 For further details of feathering see CLARK, ' The Pterylography of certain 

 American Goatsuckers and Owls,' Proc. U. S. Nat. Mns. xvii. 551. 



