1876.] ANATOMY OF PLOTLS ANHINGA. 341 



resembles that muscle in Sula and Pelecanus, being separated from 

 the obturator externus 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 elsewhere^, that in Fregata aquila the semi- 

 tendinostis 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-differentiated 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. Macgillivray in Audubon's 'Ornithological 

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

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

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

 latter viscus, be strangely savs, is soft and smooth inside. The 

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

 Macgillivray, 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 peculiarity. 



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

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

 proportionally in Pe'ecanus. 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 ylot- 

 iidis, which is evidently the rudiment of the base of the organ. The 

 hyoid cornua, 1| inch Ions, 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, Channel, and a few other birds ; but 

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

 of the organ open. This cavity communicates with the digestive 

 tube by a small orifice which is situated on the right side of the 

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

 teristic epithelium of the stomach in birds. Plate XXVIII. fig. 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 looks 

 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 



* PKfeP.Z.S. 1873. p. 636. 



t P.Z.S. 1873. p. B36. and 1*71, p. 122. 



t P.Z.S. 1*74. p. 1 Ifi § Vol. iv. p. 158. 



