101 



in Capromys than in the Acouchy, have not tbe šame proportional 

 magnitudė as in the Rat. The lachrymai bone in Capromys is very 

 small : in the Acouchy it is remarkably developed, as well as in the 

 Agouti, but it does not form any part of the external boundary of 

 the suborbital yoramen, which is exclusivly formed by the superior 

 niaxillary bone, the ungueo-maxillary suture running parallel, but 

 half a line posterior, to the anterior margin of that boundary. 

 M. Cuvier,in describing the cramMm ofihe Agouti, (Ossemens Fos- 

 eiles, vol. v. part i., p. 21,) particularly notices this large size of the 

 lachrymai bone, whlch, he statės, " contribue a entourer le trou 

 sous-orbitaire dans le haut, en sorte que l'anneau formė autour de 

 ce trou par le maxillaire n'estpas complet, ce dont je ne connois 

 point d'autre exemple:" but in exaraining, for this peculiarity, two 

 škulis of the Agouti, (which, however, it is possible may not be of 

 the identical species with the one described by the great anatomist 

 above quoted,) Mr. Ovven has notfound itin either; the whole of 

 the lachrymai bone being capable of removal without the integrjty 

 of the outer boundary of the suborbital Jbramen being thereby af* 

 fected; the lachrymai bone, however, approaches nearer in the 

 Agouti to the anterior margin of that boundary, than in the Acouchy. 

 There is also this difference betvveen the two species ; in the Agouti 

 the narrow process of the raaxillary bone which separates ihe outer 

 part of the lachrymai bone from the suborbital /bmnjen is articu- 

 lated by suture with the nasal process of the maxillary bone, aiford* 

 ing a curious example of an articulation between two parts of the 

 šame bone; in the Acouchy there is no such suture, but the whole 

 outer boundary of the suborbital yorameM is one continuous piece 

 of bone. The styloid processes are much stronger and the bony 

 meatus more produced in Capromys than in either of the before- 

 named animals. The lower jaw .of Capromys, likę that of the 

 Acouchy, is deficient in the tubercular process that is seen on the 

 middle of the outer surface of the ascending ramus in the lower 

 jaw of the Rat. 



The chief chai-acteristic of the skeleton of Capromys is seen in 

 the spinal column, and arises from the number of the dorsal or costal 

 vertehrcBy of which there are not less than 16. In the Capybara and 

 the prehensile Porcupine theve are 15, in ihe Beaver l4 ; but the 

 more common number in this order is 12, as in the Acouchy, or 13 

 as in the Rat. Notwithstanding the excess of costal vertebrce, Ca- 

 promys has the šame number of lumbar vertebrcB as the Acouchy, 

 viz. 7 ; they are also proportionally larger. The sacral vertebrce, if 

 reckoned according to form and anchylosis, amount to 4; butif con- 

 sidered as depending on the more definite character of articulation 

 with the ilia are only 2. The caudal vertebrce, if the latter mode 

 of considering the sacrum be adopted, are 22 in the specimen ; but 

 some were evidently wanting. The directions of the spines of the 

 vertebrce in Capromys indicate considerable flexibility in the trunk : 

 the principai centre of motion is marked by the erect spine in the 

 13th costal vertcbra ; in the Acouchy it is in the 12th or lašt but one. 



In the estremities the bones of tlic Capromys participate in the 



