Royal Physical Society. 387 



by a foramen, and at its anterior extremity gives attachment 

 to the carpal bones. 



The carpal bones are only two in number ; they are small 

 and linear, and support the posterior two or three of the eight 

 fin rays. The anterior rays are attached to the coracoid bone, 

 in a straight line with the transverse ridge which supports 

 the carpal bones. The fin, when in action, lies in the hori- 

 zontal plane at right angles to the body of the animal ; and 

 the support given to the posterior rays by the carpal bones 

 compensates for the slope inwards and backwards of the 

 shoulder girdle. When at rest, the fish can make the fin lie 

 alongside of its body by flexion downwards and forwards of 

 the carpal bones, which carry with them the most posterior fin 

 rays, and, with the attachment of the most anterior rays for a 

 fixed point, turn the fin round into the vertical plane. 



Vertebral Column. — Immediately behind the cranium are 

 a series of altered vertebrae, to be considered anon. They 

 are very similar in both species, and are reckoned by Dr 

 Bilharz as three in number. They are, however, four ver- 

 tebrae, as I shall show. Counting them as four, there will 

 then be, according to Dr Bilharz, twenty vertebrae of the 

 trunk, and twenty-two caudal in the Nilotic species. The 

 species which we are considering has only nineteen trunk and 

 twenty-one caudal vertebrae. The superior spinous processes 

 of the caudal vertebrse are long and pointed, as are also the 

 inferior spines ; but those of the trunk get gradually shorter 

 and thicker as we pass forward,in such a manner that the 

 tips of these processes lie in a pretty straight line from the 

 occiput to the tip of the tail. Every vertebrae, those next the 

 head excepted, presents on each side a posterior articular pro- 

 cess, projecting upwards from the posterior part of the body, 

 and a deep notch between this and the neural arch for the 

 exit of the corresponding nerve ; also an anterior articular 

 process articulating with the posterior articular process of the 

 vertebra in front, and with its neurapophysis. The spines of 

 the last caudal vertebra are united and expanded into a single 

 broad triangular plate, and the inferior spine of the vertebra 

 in front is likewise flattened. The caudal fin rays are eighteen 

 in number. The pelvic bones are slender immediately in 



