174 ON THE MORPHOLOGICAL CONSTITUTION OF 



of Joli. Miiller, on tlic " Cyclostomo'us Fishes." It becomes 

 a point of much interest to ascertain the morphological cha- 

 racter of this tubular passage, and to determine the morpho- 

 logical relations of its cartilaginous elements. 



The olfactory capsules of the myxine, bdellostoma, and 

 lamprey, are completely fused into one another at the mesial 

 plane, so as to form a single chamber, situated immediately 

 in front of, and in a line with, the cranial cavity. The 

 common olfactory chamber communicates with the cranial 

 cavity by two orifices perforated in the fibro-cartilaginous 

 transverse septum, for the passage forwards of the olfactory 

 nerves. The olfactory chamber opens below into the naso- 

 pharyngeal passage. In the lamprey this passage is mem- 

 branous throughout, the portion in front of the olfactory 

 chamber lying above the posterior superior oral shield ; its 

 posterior portion passing back between the base of the 

 cranium and the central part of the palatal cartilage, ter- 

 minates in a cul-dc-sac at its pharyngeal extremity. In the 

 myxine and bdeUostoma the posterior portion of the j)assage 

 is a membranous canal situated between the base of the 

 cranium and the mesial palatal cartilage, and opens posteriorly 

 into the pharynx. That portion of the naso-phaiyngeal 

 passage in front of the olfactory chamber is supported above 

 and laterally by a series of ten cartilaginous rings, incom- 

 plete below — the entire arrangement closely resembling a 

 mammalian trachea. The membranous floor of this part of 

 the passage is supported by the anterior portion of the central, 

 and the transverse junction of the lateral palatal cartilages, 

 and in front by the mesial and transverse superior oral 

 cartilages. 



The morphological constitution of this remarkable nasal 

 skeleton appears to be similar to that of the nasal foss£e of 

 the higher Vertebrata. The olfactory capsules have passed 

 inwards, as in the bird and reptile, so that, instead of pro- 



