764 



ANATOMY OF VERTEBRATES. 



under the lens a minutely granulated surface when the cuticle is 

 removed, which, however, is extremely thin, and has none of 

 the horny character which the claws at this period present. 

 The margins of the upper beak are rounded, smooth, thick, and 

 fleshy; the whole of the under mandible, fig. 601, g, is flexible, 

 600 and bends down upon the neck 



when the mouth is attempted to be 

 opened. The tongue, ib. A, which 

 in the adult is lodged far back in 

 the mouth, advances in the young 



601 



Young Ornithorhynchus. lxxviii'. 



Head of young Ornithorhynchus. 



LXXVIII'. 



animal close to the end of the lower mandible ; all the increase of 

 the jaws beyond the tip of the tongue, which in the adult gives rise 

 to a form of the mouth so ill calculated for suction or application 

 to a flattened surface, is peculiar to that period, and consequently 

 forms no argument against the fitness of the animal to receive 

 the mammary secretion at an earlier stage of existence. The 

 breadth of the tongue in the larger of the young specimens was 

 3 J lines ; in the adult it is only one line broader ; and this dis- 

 proportionate development is plainly indicative of the importance 

 of the organ to the young animal, both in receiving and swallow- 

 ing its food. The mandibles are surrounded at their base by a 

 thin fold of integument, which extends the angle of the mouth 

 from the base of the lower jaw to equal the breadth of the base 

 of the upper one, and must increase the facility for receiving the 

 milk ejected from the mammary areola of the mother. The 

 oblique lines which characterise the sides of the lower mandible 

 in the adult were faintly visible on the corresponding parts of the 

 same jaw of the young animal : a minute ridge of the inner sides 

 of these lines indicates the situations of the anterior horny teeth 

 of the adult. 



The exterior nostrils, ib. «, communicate with the mouth by 

 the foramina incisiva, which are situated at nearly three lines 

 distance from the end of the upper mandible, and are each 

 guarded by a membranous fold extending from their anterior 



