STEGOCEPHALIA 



123 



had been embedded in the integument. A flat, semicircular, or lunate plate, 

 interpreted as the coracoid, is placed at a slight distance behind the clavicles, 

 and there is also a narrow or rod-like piece with expanded distal extremities, 

 corresponding to the scapula of other groups. [Gegenbaur, and following him 

 G. Baur, interpret these bones differently, holding that the coracoid was in all 

 probability cartilaginous, and identifying the bone commonly known by that 

 name as the scapula, and the so-called scapula as the deithriim. The latter, as 

 shown by Gegenbaur, was attached to the distal end of the clavicle.] 



The bones of the appendicular skeleton, so far as known, agree in form, 

 number, and arrangement with those of living Urodeles. The humerus is 

 rarely furnished with articular condyles, its extremities remaining as a rule 

 cartilaginous. Ulna and radius are always separate, simple, more or less 

 elongate, and without articular faces. The carpus is imperfectly known ; in 

 many Palaeozoic genera it appears to have been cartilaginous, in others partly 

 ossified. The metacarpals and phalanges are slender and elongate. 



The pelvic arch (Fig. 206) is strongly developed, but seldom so well pre- 

 served that the form and position of all the parts are clearly distinguishable. 

 The ilium is short, 

 stout, somewhat ex- //^ 



p a n d e d a t t h e v v, 



extremities, and 

 attached to the sacral 

 ribs. Ischium and 

 pubis sometimes 

 unite to form a single 

 large plate (ischio- 

 pubis), or they may 

 remain separate. The 

 inner edges of the 

 ischia form a sym- 

 physis in the median 

 line. The pubes, 

 which are smaller, 

 sometimes remain car- 

 tilaginous amongst 

 Palaeozoic forms. 



The hind-limb is 

 almost always more 

 strongly developed than the fore-limb. The femur is a strong, elongate bone, 

 without an ossified capitulum, but often with well-formed distal condyles. 

 Tibia and fibula remain separate, and resemble the corresponding bones of 

 the anterior limb. The tarsus is either cartilaginous or composed of two 

 rows of small bones. The pes is provided with five digits, but is otherwise 

 closely similar to the manus ; sometimes the second digit is the longest, in 

 other cases the third. 



Habitat. — The mode of occurrence of Stegocephalians in the Coal Measures, 

 Lower Permian, and Keuper, indicates that they were either freshwater 

 inhabitants, or terrestrial forms. Some of the smaller genera appear to have 

 sequestered themselves in hollow tree-stumps, since in ISTova Scotia, at least, 

 their remains are commonly found in cavities of decayed Sigillaria and 



Pelvic arcli of Mastodonsaurus giganteus, Jaeg. (after Praas). 

 1, Iliuin ; IscJi, Ischium ; Pu, Pubis ; Ac, Acetabulum. 



