10^ 



characters both of the Rat and Acouchy; those of the anterior ex- 

 tremity presenting, in addition to the perfect clavicles, some other 

 characters in common with the former, while those of the posterior 

 more resembled the corresponding bones in the Acouchy. Thus in the 

 scapula the acromion, as in the Rat, projects beyond the glenoid ca- 

 vity to join tiie clavicle, and the coracoid process is well developed ; 

 while in the Acouchy the former process is much less ])roduced, and 

 the latter almost obsolete. In the descending process of the acro- 

 wion, Capromys, like Cceloge?ius and Hystrix, is intermediate be- 

 tween the Rat and the Acouchy. The humo-us of Capromys is pro- 

 portionally stronger than in the Acouchy, and it has the deltoid pro- 

 cess even more developed than in the Rat; this process is but slightly 

 indicated by a ridge in the Acouchy. The internal condyle, like that 

 of the Acouchy, the Rat and most Rodentia, is imperforate. The 

 rest of the bones of the anterior extremity aftbrded no peculiar 

 characters. 



Passing over the bones of the pelvis, which also were destitute of 

 any marked character, Mr. Owen observed that the Jeinur of Ca- 

 promys, like that of the Acouchy, has no middle process or second 

 trochanter, such as is observable in the Rat and Beaver. The tibia 

 and ^fibula were also distinct in Capromys, as in the Acouchy; the 

 latter bone reaching to the tarsus, and not being, as in the Rat and 

 Beaver, anchylosed to the lower third of the tibia. The metatarsal 

 bones of Capromys agree in number with those of the Rat, but are 

 broader and flatter, and correspond to the more plantigrade cha- 

 racter of this animal. 



Mr, Owen concluded his remarks on the osteology of these ani. 

 mals by presenting the following table, in which the points of ad- 

 measurement are for the most part the same as are used by Mr. 

 Say, in his account of Capromys {Isodon) Pilorides (Journal of 

 Acad, of Nat. Sci. of Philadelphia, ii, p. 334.). 



Cranium. 



From the anterior edge of the sockets of 

 the incisors to the posterior part of 

 the occipital condyles 



From ditto to the posterior part of the 

 occipital crest 



Distance between the remotest points of 

 the zygomatic arches 



Shortest distance between the orbits . . 



Length of a series of molar teeth .... 



Width of the largest molar tooth .... 



Vertical diameter o^ i\\e foramen magnum 



Transverse diameter of ditto 



Vertical diameter of the suborbital /c;;«- 

 mcn (anteriorly) 



Ditto of the orbit ..... r-» 



