THE REPTILIAN CLASS OF THE MOSASAURIDiE. 711 



As to the " many Lacertilia without limbs," the facts are as fol- 

 lows : — 



In 344 genera of Laeertilia, scapular and pelvic arches with 

 well-developed digitate fore and hind limbs are present and func- 

 tional in locomotion : in about 23 genera, the limbs are so reduced 

 in size as to take little if any share in active locomotion ; still they 

 are limbs, are conspicuous in most of these as such, and do not need 

 dissection to demonstrate them. The genera where they may be termed 

 rudiments are extremely few. The limbs are very short in Chalcis and 

 Sauropus ; but there they are, and attached, moreover, respectively 

 to a scapular arch and to a pelvic arch. The fore pair may be in- 

 conspicuous or wanting, as in Psendopus ; but the scapular arch is 

 there, and the diminutive hind limbs have their pelvic arch. Both 

 arches, moreover, are represented in Lacertians (Anguis, Aprasia, 

 e. g.), where the limb appendages are gone. 



How stands the statement that some Serpents have limbs ? 



In certain Ophidia dissection has revealed a small styliform bone 

 on each side the cloaca ; in a few it is tipped with horn in the shape of 

 a claw ; this is externally conspicuous in Python, and is serviceable, 

 where so developed, in the act of coition. Whether these appendages 

 to the generative parts be homologous with the " claspers " of 

 sharks, or with the ventral fins, and if the latter, with the hind limbs 

 of Lizards, is yet an open question *. 



But as unquestionable fore and hind limbs are the rule in 

 Laeertilia, and the questionable and outwardly visible rudiments of 

 the hind pair are exceptional in Ophidia, the presence of both a 

 fore pair and hind pair of limbs in the Mosasauroids is relevant, 

 and will so be held, to the problem of the nature and affinities of 

 those marine Reptilia. 



§ 10. Teeth. — Prof. Cope, in his characters of Pythonomorpha, 

 gives, as the 17th : — " The teeth possess no true roots " f. In the 

 subsequent descriptive expansion of this character, he writes : — " The 

 crowns are covered with enamel, and their forms indicate the carni- 

 vorous habits of these reptiles " J. 



The teeth of Mosasauroids have an enamelled crown and cement- 

 clad root. The enamel develops a pair of opposite low ridges 

 which are minutely crenate : the crenation becomes abraded at the 

 apical part of used teeth, but is demonstrated in unworn and unex- 

 tricated crowns. Many Saurians, both Crocodilian and Lacertian, 

 show the creno-bicarinate character ; but no Ophidian does. I do 

 not dwell upon the formal differences between the Mosasauroids and 

 Ophidians in the proportions of length, breadth, and thickness of 

 the dental crown, the structural difference being more decisive. The 

 speedy confluence of the radical cement with the surrounding bone, 

 and the thickness of the osseous mass so resulting and forming the 

 broad conical base of the tooth, are features of resemblance to the 

 Lacertians called " acrodont ;" but the way and degree in which the 



* " Some cold-blooded vertebrates, e. g. Muramoids and Ophidians, have 

 neither fore nor hind lirabs."— Anat. of Vertebrates, vol. i. p. 179. 

 t Op. cit. p. 114. | Op. cit.ip. 116. 



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