98 Mr. Brookes on a new Genus of the Order Rodeniia, 



as scarcely to be capable of scientific description, is strongly 

 opposed to the very simple form of those of Lagostomus, which 

 present only three parallel lines of enamel, separated by two 

 intervening portions of the osseous part of the tooth. 



The rami of the lower jaw are arched, broad, and strong, and 

 exhibit very distinctly on their under surface the roots of the 

 molar teeth, and also the course of the incisors within the bone : 

 the angle is very much produced posteriorly : the plate is broad, 

 and is deeply grooved above, behind the molar teeth : the co- 

 ronoid process is very acute ; the condyle elongated from before 

 backwards, and the glenoid cavity large, and extended con- 

 siderably in the direction of the condyle. 



As all the Mammalia have seven cervical vertebrae, with the 

 exception of the Sloth, which has nine, there cannot be any 

 necessity for referring to those bones for numerical comparison 

 with those of other animals. The number of ribs, and con- 

 sequently that of the dorsal vertebrae, is twelve on each side; 

 that of the lumbar, seven : in both these particulars Lagostomus 

 agrees with the Jerboa. The sacral vertebrae of Lagostomus are 

 three, and the caudal twenty. 



The anterior extremity is comparatively shorter than in the^ 

 greater number of the Rodentia, but is longer and stronger than 

 in the Jerboa. The clavicle is complete. The scapula is rather 

 delicate ; its spine is but slightly elevated ; and the acromion is 

 slender, flattened, and considerably elongated, equalling in length 

 the remaining portion of the spine. The os brachii is strong, has 

 a considerable tubercle at its outer surface somewhat below the 

 head of the bone, and exhibits a tendency to expand into a 

 ridge (the processus deltoides). The condyles are lengthened 

 transversely, and are widely separated. The radius is about 

 one-fourth longer than the os brachii, and it inclines towards 

 the ulna, which is anchylosed anteriorly with it through about 



two- 



