16 



oesophagus. There exists, then, a fundamental anatomical difference 

 between these parts, whatever else may be their physiological functions, 

 and this difference furnishes a fresh argument in favor of the opinion of 

 those who consider the Lepidosiren as a reptile." 



The resemblance of the air-bladder of the Polypterus to the pulmonary 

 sacs of Lepidosiren has been justly insisted on by Owen. The air-blad- 

 der of Polypterus is described by him as being double, consisting of two 

 long cylindrical lobes, but of unequal length, the left being the longest, 

 and extending through the whole length of the abdomen. It has also 

 been stated to communicate by an elongated fissure with the ventral floor 

 of the throat. The fissure is also said by Geoffroy St. Hilaire to be pro- 

 vided with a constrictor muscle. 



There is then no fundamental difference between the pulmonary sacs 

 or air-bladders of the Lepidosirenoids and the Polypteroids. If Lepido- 

 siren is to be regarded as an Amphibian on account of the communica- 

 tion of the pulmonary sacs with the inferior face of the intestinal canal, 

 then, for the same reasons, the Polypteroids are to be considered as Am- 

 phibians. But the affinities of the Polypteroids with the Lepidosteoids 

 of America are undeniably very great ; the latter have the lung-like air- 

 bladder communicating by a long fissure with the upper region of the 

 oesophagus, and thus agree with the fishes. The comparatively slight 

 importance of that character alone in determining the classification of 

 Lepidosiren is then evident. 



It is a fact of no little interest that the Polypteri, which have an air- 

 bladder so similar to that of the Lepidosirenes, do also, of all known fishes, 

 most resemble them in the form and development of the different elements 

 of the brain. 



The attachment of the scapular arch directly to the skull is one of the 

 strongest evidences of the pertinence of the Lepidosirenoids to the class 

 of Fishes. The Protopterus annectens is asserted by Owen to have "the 

 scapular arch directly suspended to the skull, but with this peculiarity, 

 that it is connected by a synovial joint with the exoccipitals only." It is 

 the fact of suspension of the scapula to the skull that is of value in this 

 case ; the manner or means by which it is suspended is abnormal, and 

 does not occur in other fishes. Professor Owen has then remarked that 

 " in all osseous fishes, and in those Ganoids, as the Sturgeons, e. g., that 

 come nearest to the Lepidosiren in some parts of their structure, the 

 scapula is suspended by two processes to the paroccipital and to the 

 mastoid." 



The jointed pectoral and ventral filaments of Protopterus still further 

 indicate the affinity of Lepidosirenoids to the fishes. Those of the so 

 called Rhinocryptis amphibia have been described by Peters as not 

 merely consisting of single articulated rays, " but also of cartilaginous 

 rays which emanate from the inferior margin of the main limb or principal 

 ray of the fin, and to which still finer cartilaginous filaments are attached. 



