200 



LECTURE VIII. 



aorta, along the back of the abdomen, into the hoBmal canal ; com- 

 municate, in their course, with the ventral branches of each of the 

 spinal nerves ; supj^ly the kidneys, the generative glands, and the 

 urinary bladder, where this exists ; and often, finally, blend together 

 into a common trunk beneath the tail. Ganglions are sometimes 

 found at the junction of the sympathetic with the fifth, as well as at 

 that with the glosso-pharyngeal and with the vagus, before the great 

 splanchnic is formed : small ganglions are more rarely discernible at, 

 the junction of the sympathetic with the spinal nerves. 



The splanchnic ganglion of the Skate is a large fusiform body, of 

 an ash-red colour ; the succeeding ganglia on the trunks of the sym- 

 pathetic are larger and more constant than in Osseous Fishes ; but 

 the intervening chords are semi-transparent.* 



Special Organs of Senses. 



The essential character of the Organ of Smell in fishes is, that the 

 pituitary membrane lines the concave wall of 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 respira- 

 tory medium in its course to the respiratory organs. 



The extremities of the olfactory nerves {Jig. 54, 55. i) 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 ' {Jig. 30. 19). 



In the Dermopteri the olfactory organ is single : Dr. Kolliker f 

 regards as such a small, blind, tegumentary depression {Jig. 46. ol), 

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

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

 factoi'ily determined olfactory organ of the Ammocete is in the 

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

 {Jig. 25. 19), whence a narrow canal is produced backwards from the 

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

 rietes of the olflictory canal are similarly situated, lined by a longi- 

 tudinally-plicated pituitary membrane, and are strengthened by 

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

 backwards upon the roof of the mouth ; and this opening is provided 



* LIV. 



f XXXII. p. ;V2. pi. ii. fig. 5 A : it should be looked for over the left eye-speck. 



