No. 2300. 



SKELETON OF DIMETRODON GIGAS—GILMORE 



533 



have suflPered more or less loss from their upper ends, but none show 

 any expansion of this end as in Edaphosaurus; all probably tapered 

 to a pointed end with cupped extremity. 



Several of the spines as shown in plate 71 have large exostoses 

 showing that they have been 

 broken and healed during life. 



Rihs. — Parts of nearly all the 

 ribs are present, of which six 

 are complete. None were found 

 articulated, so that their present 

 position in the skeleton is based 

 entirely on a study of their rela- 

 tive size, spread of head between 

 capitulum and tuberculum as 

 compared with the vertebral ar- 

 ticulating facets. Counting back 

 from the axis, ribs Nos. 7, 9, 10, 

 and 1 1 of the right side, and Nos. 

 7 and 16 of the left side are 

 perfectly preserved. 



The anterior thoracic ribs when 

 articulated form a much flattened 

 and exceedingly deep body cav- 

 ity immediately behind the fore- 

 legs. (See pi. 72, fig. 1.) More 

 posteriorly, however, the ribs 

 take on a decided convexity, as 

 may be seen by comparing ribs 

 A and B, figure 4. All of the 

 thoracic ribs are terminated dis- 

 tally by slightly expanded cylin- 

 drical ends that are cupped for 

 the better attachment of the 

 cartilagenous ribs of the belly. 



There was no evidence of the 

 presence of ossified abdominal 

 ribs. The seventh pair of ribs, 

 the longest of the entire series, 

 measure 395 mm. in length. The 

 sixteenth rib of the left side is 

 334 mm. long measured from the tuberculum over the curve. 



Shoulder girdle avd fore limh. — In his monographic work, "The 

 Pelycosauria of North America," » page 121, Case says: "The 

 shoulder girdle of Dimetrodon gigas unknown." It is, therefore, of 

 interest to find with specimen No. 8635, U.S.N.M., the complete 



Pub. 65, Carnegie Institutton of Washington, 1907. 



Fig. 4.— Ribs of Dimetrodon gigas, No. 8635, 



U.S.N. M. A, SEVENTH rib of RIGHT SIDE, 

 VIEWED FROM THE FRONT; B, SIXTEENTH RIB OF 

 LEFT SIDE, (REVERSED) VIEWED FROM FRONT; 

 C, MEDIAN CERVICAL RIB; C, CAPITULUM; t., 

 TUBERCULUM. ALL FIGURES ABOUT ONE-THIRD 

 NATURAL SIZE. 



