376 



2074. The separated bones of the skull of an Agouti (Dasyprocta Aguti}. 



The bones are numbered on coloured labels, to correspond with the TABLE OF SYNONYMS. 



The basisphenoid, presphenoid, and their respective alee have coalesced into a single bone ; 

 but the pterygoid remains united by suture to the ectopterygoid and entopterygoid processes 

 of the alisphenoid ; and, by its union with the ectopterygoid process, an interpterygoid canal 

 is formed, which is completed, as will be seen in the Porcupines, by the entopterygoid plate. 

 Bristles are passed through the minute entocarotid canals, which perforate the sides of the 

 basisphenoid near its back part. The alisphenoid is directly perforated by the foramen ovale, 

 but there is neither an ectocarotid nor an alisphenoidal canal. 



Presented by Prof. Owen, F.R.8. 



Family Hystricidce (Porcupines). 

 Genus Ilystrix. 



Dental formula : i |=j, p {, m 15= 20. 



2075. The skeleton of the Crested Porcupine (Ilystrix cristata}. 



It is of a female, and not quite adult, some of the epiphyses being still ununited. The ver- 

 tebral formula is : 7 cervical, 15 dorsal, 4 lumbar, 4 sacral, and 12 caudal. Eight pairs of 

 ribs directly join the sternum, which consists of seven bones. The potential base of the acces- 

 sory processes begins to be developed upon the fourth dorsal, and divides upon the eleventh 

 into the anapophysis and metapophysis. The distinction of both these processes from the 

 diapophysis, which supports the last floating rib, is well marked in the last dorsal vertebra. 

 In the lumbar vertebrae the anapophyses strengthen the joints by underlapping the metapo- 

 physes, but both processes become rudimentary in the last lumbar. The two anterior sacral 

 vertebrae support the ilia. The hinder half of the upper costa of the scapula is straight and 

 nearly parallel with the lower costa : the base is slightly curved, and at almost right angles 

 with the costse. The supraspinal fossa is broader than the infraspinal one, the spine inclining 

 downwards or backwards and the acromion being bent in the same direction. The part 

 answering to the descending process in the Cavies appears here to form a direct prolongation 

 of the acromion, its true anterior extremity forming only an obtuse angle. The humerus has 

 a large vacuity between the condyles, but no perforation above the inner condyle. The cla- 

 vicular bones have not been preserved in this specimen. 



Mils. South. 



2076. The skull of a male Porcupine (Hystrix cristata). 



The occipital region is nearly flat, and inclines from below upwards and a little forwards. 

 The paroccipitals descend nearly to the level of the lower part of the occipital condyles. The 

 mastoid forms only a rough ridge. The auditory bullae are moderately developed : the 

 external meatus is short, directed outwards and a little forwards, and is notched behind. A 



