BOOM IV. PADDLES OF THE ICHTHYOSAURUS. 373 



bine with the ischium and pubis to form the acetabulum, or 

 socket for the femur. Professor Owen has directed especial 

 attention to the fact, that " its upper or proximal end is not 

 connected by syuchondrosis to the extremities of the sacral 

 ribs, but lies simply upon them, just as the scapula rests 

 upon the ribs at the anterior part of the thorax. This is a 

 condition of the ilium which is of great interest, and pecu- 

 liarly characteristic of the Enaliosauria, among reptiles. It 

 renders their pelvic extremities remarkably analogous to the 

 ventral fins of fishes, which are in like manner simply sus- 

 pended in the muscular mass, and not fixed to a sacrum." l 



PADDLES, AND INTEGUMENTS. The extremities or limbs of 

 the Ichthyosaurus, with the general structure of those of the 

 Plesiosaurus, have the humerus, femur, and the antibrachial 

 bones, relatively shorter and broader. The carpus and tarsus 

 are composed of polygonal bones, which are succeeded by 

 several longitudinal rows of similar ossicles ; and the re- 

 mainder of the paddle is made up of a gradually diminishing 

 series of the same character. 



An unexpected light has been thrown upon the original 

 structure of the paddles of the Ichthyosaurus, by the discovery 

 of a specimen with remains of the integuments in a carbon- 

 ized state ; and so admirably preserved, as to demonstrate 

 that the fin extended far beyond its osseous frame-work, and 

 was bordered by cartilaginous rays, which bifurcated as they 

 approached the margin. 



Lign. 76, is a reduced figure of the hinder paddle of an 

 Ichthyosaurus, (/. communis), with the integuments preserved, 

 from the plate accompanying the original memoir on this 

 fossil, in the " Geological Transactions." The specimen, which 

 was discovered by Sir Philip Egerton, consists of the pha- 

 langeal bones of a posterior paddle, with the soft parts, or 

 integuments, lying together in their natural position ; , marks 

 the termination or distal extremity of the fin, consisting 

 entirely of the carbonized integuments ; these gradually widen 

 and expand to receive the terminal rows of the phalangeal 

 ossicles or bones, marked, 6. The upper border of this soft 



1 " Brit. Assoc. Rep." 1839, p. 107. The admirable exposition of the 

 osteological characters of the Ichthyosauri contained in this Report 

 should be consulted by the palaeontologist who is interested in the 

 subject. 



