1876.] ANATOMY OF PLOTUS ANHINGA. 341 



resembles that muscle in Sula and Pelecanus, being separated from 

 the obturator extermis by a well-marked interval, which is not the 

 case in Phalacrocorax* . It is to be remembered, as I have had the 

 opportunity of stating elsewheref, that in Fregata aquila the semi- 

 tendinosus is entirely absent, as in the Accipitres, whilst in Phaethon 

 It has an accessory head as well as a considerable bulk itself, these 

 facts tending strongly to verify Brandt's division of the Steganopods + 

 into three well-aifferentiated groups, of two of which the two above- 

 named genera are the only examples. 



^ The alimentary canal of the Darter presents features of especial 

 interest, as in its stomach there is a modification in the structure of 

 the proventriculus not referred to in zoological works generally. It 

 is fully described by Mr. Macgillivrav in Audubon's 'Ornithological 

 IJiography' §, where an excellent figure illustrates the account. Mr. 

 Macgilhvray also accurately describes most of the other viscera. He, 

 however, omits to refer to the hairy mat in the second stomach, which 

 latter viscus, he strangely says, is soft and smooth inside. The 

 observations here made, which are in accordance with those of Mr. 

 Macgilhvray, cannot be considered de trop, as the extremely abnor- 

 mal conformation he describes required verification before 'it could 

 be accepted as not being merely an individual peculiaritj . 



The tongue, as an independent organ, dues not exist. It is very 

 small in all Steganopods, but free at its anterior extremity ; smallest 

 proportionally in Pelecanus. In Plotus, however, it is' not free at 

 Its apex, It forming merely a longitudinal groove along the middle of 

 the floor of the mouth, and ending abruptly behind by a small trans- 

 verse slightly projecting ridge, 2^ inches in front of the rima glot- 

 tidis, which IS evidently the rudiment of the base of the organ. The 

 hyoid cornua, 1^ inch long, running in the faucial membrane, here 

 meet and blend. 



There is no crop ; the oesophagus, however, is very dilatable. The 

 proventriculus does not form a zone, as is the rule : nor does it form 

 a patch, as in Struthio, Rhea, Chauna, and a few other birds; but 

 it forms a special gland-cavity into which the individual constitueuta 

 of the organ open. This cavity communicates with the digestive 

 tube by a small orifice which is situated on the rigiit tide of the 

 stomach, just below the commencement of the yellow dense charac- 

 teristic epithelium of the stomach in birds. Plate XXVIII. fio-. 2 

 will assist in rendering this explanation more distinct. "' 



The proventricular compartment is covered by peritoneum, is nearly 

 globose, about the size of a chestnut, and fixed to the right side of 

 the lower end of the oesophagus. On superficial inspection it looka 

 very like an enlarged spleen (that organ being subglobose in birds). 

 Its cavity is very small, being much encroached upon by the great 

 depth of the cylindrical glands which compose its walls. The yellow 

 stomach-epithelium surrounds its orifice and goes no further. There 

 are no indications of additional proventricular glands at the lower 



* TtV/c P. Z. S. 1873. p. 63R. 



t P.Z.S. 1873, p. 636, and 1874, p. 122. 



t r. Z. 8. 1^74. p. 116. § Vol.iv.p.l.'^S. 



