THE AFRICAN MUD-FISH. ID 



about the same length, and all short ; they are bent downward in the tail, so as to form an inferior 

 arch like the neural arch, after the manner which is usual in fishes. The skull is penetrated by the 

 cranial end of the notochord, though it there becomes ossified. The skull is divided into distinct 

 cranial segments, each formed of bones. The lower jaw consists of two pieces a dentary bone in 

 front and the articular bone behind. The jaws are armed with two slender conical teeth on the 

 pre-maxillary bones, and with a strong dental plate on both the lower and upper sides of the mouth. 

 These teeth are marked with ridges, and were originally compared by Sir R. Owen to the teeth 

 of Ceratodus then supposed to be extinct and the teeth of Chimsera. There are no teeth on the 

 bones of the palate. 



The intestine is straight and short ; it terminates in a spiral valve formed of six gyrations. The 



AFRICAN MUD- FISH. 



vent does not open in the middle line of the body. There is no trace of a pancreas or spleen, but 

 the dark-brown liver has a gall-bladder in a notch of its left margin. The bile is conveyed by a 

 duct into the intestine. The brain closely resembles that of Amphibians. This genus is dis- 

 tinguished by possessing six branchial arches with five intervening clefts, and has three small 

 branchial appendages above the small gill-opening. The air-bladder has a longitudinal partition, 

 so as to divide it into two elongated sacs, which are supplied with venous blood from a pulmonary 

 artery. Each of these sacs is divided into cells, which are more numerous in the fore-part of the 

 bladder than in the hinder part. It is by means of these incipient lungs that respiration is carried 

 on during the dry months, when the animals live out of water. Air is introduced directly into the 

 air-bladder, and the opening of the duct from it into the oesophagus is kept distended by a cartilage 

 like a rudimentary larynx. When, in the wet season, the Lepidosiren resumes life as a fish, the 

 branchial circulation again goes on vigorously, but the animal still rises to the surface and swallows air. 

 The Protopterus exhibits the simplest form of limb which is known. The pectoral and ventral 



