330 Richard Owen, Esq., on Comparative Osteology. 



general homologies. Final purpose of the modifications of the cranial 

 bones in Fishes. 



Lecture vi. — Skeletons of the Batrachia. — Biconcave vertebras 

 of the perennibranchiate species: simplification of the skeleton as 

 compared with that of Fishes. Cup-and-ball vertebrae of the caduci- 

 branchiates : reduction of the number of vertebras in the anourous 

 family. Determination of the bones of the head. Pectoral and 

 pelvic extremities. Key to the nature of the pelvis afforded by that 

 of the Menopome. Metamorphosis of the skeleton of the frog. 

 General observations on the Batrachian skeleton. Its character- 

 istics determine the nature of gigantic extinct species. 



Lecture vii. — Skeletons of the Ophidia : — Characterised by the 

 vast number and peculiar complexity of the vertebrse. Their pro- 

 cesses and modifications in different species and different parts of the 

 vertebral column. Ribs hollow, moveable, without sternal ribs or 

 sternum. Long cervical hypapophyses, which form oesophageal 

 teeth in the Deirodon scaher. Density and strength of the overlap- 

 ping cranial bones : mobility of the maxillary, mandibular and 

 palatine bones : modification of the upper jaw in poisonous serpents. 

 Rudimentary scapular arch in Anguis. Vestiges of hinder limbs. 

 Large fossil serpents. Compensations for absence of prehensile or 

 ambulatory limbs. 



Lecture viii. — Skeletons of Lacertilia. — Easy transition from 

 Serpents to Lizards. Same procselian type of vertebrse in both : 

 their modifications in the cervical, dorsal, lumbar, sacral and caudal 

 regions. Modifications of the atlas, illustrated by that in extinct 

 Saurians. Structure of the skull in Lizards. Complex scapular arch. ' 

 Locomotive extremities. Costal parachute of Draco Volans. True 

 wings of extinct Pterodactyles. 



Lecture ix. — Skeletons of Crocodilia. — Osteological distinctions 

 between Crocodiles and Lizards. Characteristics of the vertebrse in 

 different regions of the Crocodile. Determinations of the bones of 

 the head. Complex eustachian canals. Scapular and pelvic arches 

 and extremities. Illustrations of the extinct Eeptilian orders of 

 Dinosauria and Enaliosauria. 



Lecture x. — Skeletons of Chelonia. — Solid texture of the bones 

 in this order. Structure, development and homologies of the cara- 

 pace and plastron. Peculiarities of the cervical vertebrse. Bones of 

 the head. Edentulous beak-shaped jaws. Modifications of the skull 

 in marine and terrestrial species. Scapular and pelvic arches and ex- 

 tremities. Antiquity of the chelonian modifications of the vertebrate 

 skeleton, and their manifestation by extinct species of gigantic size. 



Lecture xi. — Skeleton of Birds, essentially a modification of the 

 Saurian type. Texture and general characters of the bones. De- 

 velopment and extent of the air-cells in the skeleton : ratio of pneu- 

 maticity of the bones to the powers of flight. Rapid and complete 

 ossification. Extensive anchylosis of the bones. Characters of the 



