372 



Genus Dasyprocta. 

 Dental formula : i |=J, p \=, m ^=20. 



2046. The skeleton of the Acouchy (Dasyprocta Acuchy). 



The vertebral formula is : 7 cervical, 13 dorsal, 7 lumbar, the last having the characters 

 of a sacral vertebra on the left side, 4 succeeding vertebrae are anchylosed to form the 

 sacrum, and there are 14 free caudal vertebrae. The spine of the twelfth dorsal is that 

 towards which those of the other trunk-vertebrae converge. The metapophysial ridge begins 

 to be developed above the diapophysis of the ninth dorsal, and is divided into the anapophysis 

 and metapophysis in the eleventh dorsal. The anapophysis is small upon the succeeding 

 vertebrae, and disappears in the last lumbar. The metapophysis is better developed, and 

 continues throughout the lumbar vertebrae. Eight pairs of ribs directly articulate with the 

 sternum, which consists of nine bones, a distinct episternal being articulated to the anterior 

 end of the manubrium. The axis vertebra is carinate, with a tubercle beneath. The trans- 

 verse processes of the last cervical are perforated and bifid. There are no clavicles in this 

 skeleton, but in two recent specimens dissected at the Zoological Society, slender clavicular 

 bones, eight lines in length, were detected. The supraspinal and infraspinal fossae are of 

 equal depth. The acromion is long, slender, and expands into a triangular plate at its 

 extremity. The humerus is perforated between the condyles, but not above the inner con- 

 dyle. The radius and ulna have become anchylosed together, and the interosseous space is 

 reduced to a narrow chink near their proximal ends. The fore foot is pentadactyle ; the 

 hind foot tridactyle. The femur gives a feeble indication of a rudiment of the third trochanter 

 at the middle of its outer side. The long entocuneiform bone has coalesced with the inner 

 side of the metacarpal of the second toe, here the innermost. The supplementary ossicle 

 crossing the articulation between the astragalus and scaphoides is present. Both scaphoid 

 and cuboid bones send strong processes to the plantar side of the tarsus. 



Hunterian. 



2047. The skull of an Agouti (Dasyprocta Aguti). 



The clamping posterior prolongation of the squamosal begins here to increase in breadth, 

 and only a narrow fissure is left between its lower border and the tympanic, communicating 

 with the cranial cavity. The sagittal suture is obliterated : the frontal one is retained. The 

 temporal fossa, though small, begins to be more distinctly defined from the orbit by a post- 

 orbital process, formed by the postfrontal and squamosal. The zygoma is short and slender ; 

 its curvature being chiefly downwards. The antorbital vacuity is wide, and circumscribed 

 externally by the zygomatic process of the maxillary, which is united by a suture to the nasal 

 process of the same bone. The lacrymal is largely developed, perforated at its inner part, 

 and forming a broad triangular plate in front of the orbit. The premaxillaries are large and 

 subquadrate : their nasal angles are not produced so far back as the nasals themselves are. 

 The meatal aperture of the auditory bulla is deeply notched at its lower border. A small, 

 distinct, crescentic grooved ossicle for the support of the tympanic membrane is preserved 

 and artificially attached to the right meatus auditorius. The posterior half of the lower 



