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2013. The maxillary and premaxillary bones, with the teeth (excepting the last 

 molars), of the Ctenomys Magellanicus. 



The rhinencephalic part of the cranium is preserved. 



Presented by Captain King, R.N. 



2014. The left ramus of the lower jaw of the Ctenomys Magellanicus, with the 

 implanted parts of the teeth exposed. Presented by Captain King, R.N. 



2015. The facial part of the skull of the Ctenomys JBraziliensis. 



The interorbital part of the frontals is flat, with the superorbital ridges slightly raised 

 above its level. The nasal bones are longer in proportion to their breadth, and straighter 

 than in the Magellanic species. A portion of the narrow lacrymal is preserved with the 

 antorbital process of the frontal and the attached process of the maxillary. 



Presented by Charles Darwin, Esq., F.R.S. 



Genus Lagotis. 



2016. The cranium of Cuvier's Chinchilla (Lagotis Cuvieri}, wanting the basi- 

 sphenoid. 



The mastoid portion of the large tympanic bulla rises to the upper surface of the cra- 

 nium as in the true Chinchilla, hut it is completely girt by a process of the superoccipital, 

 which extends outwards to articulate with the extremity of the slender process of the 

 squamosal. The vacuity which intervenes between* the alisphenoid, parietal, and tympanic, 

 and which, in other Mammalia, is closed by the more expanded squamosal, is here, through 

 the retention by that bone of its primitive form as a diverging slender ray, left uncovered. 

 The meatus is long, wide, infundibuliform, with the outlet obliquely truncate and directed 

 upwards and a little backwards : the petrosal bulla, continued from its lower extremity, 

 seems to describe a semicircular curve downwards and backwards, circumscribing the large 

 foramen, which directly pierces the bulla beneath the meatus. The paroccipital is slender ; 

 its point does not extend below the level of the tympanic bulla. The articular groove for th 

 lower jaw is deep, and is completed externally by the malar. An almost circular piece seems 

 to be cut out of the zygoma, above the junction of the malar with the squamosal. The facial 

 part of the lacrymal extends half-way across the antorbital root of the zygoma, where the 

 zygomatic part of the maxillary articulates by suture with the nasal process of the same 

 bone, circumscribing a large antorbital vacuity. The nasal processes of the premaxillaries 

 slightly expand at their extremities, which extend beyond the corresponding ends of the 

 nasals. A strong and long oblique ridge traverses the inner side of the ramus of the lower 

 jaw. The outer side is irregularly swollen by the bases of the sockets of the curved molars, 

 but has not the distinct ridge which characterizes that part in the Cavies. 



Presented by J. B. Pentland, Esq. 



