328 ANATOMY OF VERTEBRATES. 



mydas) the tongue is wrinkled and devoid of papillae. In the 

 Crocodiles the tongue has no projecting extremity, and is but 

 slightly raised above the level of the membrane which attaches its 

 circumference to the mandible : but its dorsum is marked by a 

 group of follicles and increased vascularity of that part of its 

 surface. 



63. Organ of Smell in H&matocrya.- -The essential character 

 of the organ of smell, in Fishes, is the pituitary membrane lining 

 a sac with one or more apertures upon the external surface ; and 

 that, in the few exceptions in which it is extended into a canal 

 communicating with the mouth or fauces, such naso-palatine canal 

 is never traversed by the respiratory medium in its course to the 

 respiratory organs. 



The extremities of the olfactory nerves, fig. 203, o, expand 

 upon the pituitary membrane, which is highly vascular, and is 

 covered by ciliated epithelium : its extensive surface is packed 

 into the small compass of the olfactory capsule by numerous folds. 

 The capsule is formed by a fibrous membrane, which is sometimes 

 supported by a cartilaginous, and more frequently by an osseous, 

 basis, called the ' turbinal bone,' fig. 81, 19. 1 



In the Dermopteri the olfactory organ is single : Kolliker 2 

 regards as such a small, blind, tegumentary depression, fig. 169, o/, 

 beset with vibratile cilia, and connected with the anterior end of 

 the quasi-brain of the Branchiostoma. The more obvious and 

 satisfactorily determined olfactory organ of the Ammocete is in the 

 median line, opening above the mouth in front of the brain-sac, 

 fig. 59, 19, whence a narrow canal is produced backward from the 

 bottom of the sac to the base of the skull. In the Myxine the 

 parietes of the olfactory canal are similarly situated, lined by a 

 longitudinally-plicated pituitary membrane, and are strengthened 

 by cartilaginous rings, like a trachea. The naso-palatine tube 

 opens backward upon the roof of the mouth, and this opening is 

 provided with a valve. In the Lamprey the flask-shaped nasal 

 sac, fig. 61, k, opens upon the top of the head : a simple mem- 

 branous tube is continued from the expanded bottom of the sac, 

 which dilates as it descends, but terminates in a blind end at the 

 hypophysial vacuity, fig. 60, hi/, of the base of the skull, where 

 the mucous membrane of the palate passes over it entire and 

 imperforate. 3 



In all Fishes, save the Dermopteri) the olfactory organs are 

 double, and they have no communication with the mouth. In 



1 LIV. 2 xxxn. p. 32, pi. ii. fig. 5, A. 3 xxi. pi. 43, figs. ii. & iv. 



