373 



border of the mandibular ramus forms an outwardly projecting ridge extending from beneath 

 the first molar to the backwardly produced angle of the jaw. 



Hunterian. 



2048. The skull of a young Agouti (Dasyprocta Aguti). 



The superoccipital, not having coalesced with the other elements of the ' occipital bone,' is 

 lost. The teeth have been removed from the right side of both upper and lower jaws and 

 are separately displayed. The molar series is -^^ the first being the deciduous molar ; its 

 successor the premolar and the last true molar are concealed in their formative alveoli : the 

 upper deciduous molar has three diverging fangs, the lower one has two ; the base of the first 

 and second true molars has just begun to divide into fangs. 



Hunterian. 



2049. The skull of an older Agouti, with the mature dentition. 



The sutures between the superoccipital and exoccipitals are not quite obliterated. The 

 teeth have been removed from the left side of both jaws and separately displayed. 



Hunterian. 



2050. The skull of an Agouti, longitudinally bisected. 



The petrosal is deeply impressed by the lateral appendage of the cerebellum : the ridges 

 defining the rhinencephalic and epencephalic chambers are well marked. 



Presented by Capt. King, R.N. 



2051. The cranium of an Agouti, in three transverse sections. 



The posterior section shows the epencephalic and acoustic chambers ; into the latter the 

 cochlea projects, its base being applied over the lower division of the internal auditory 

 passage : the cochlear canal describes three gyrations, in which the lamina spiralis is exposed : 

 the short and wide ' meatus auditorius externus ' terminates in an expanded hoop for the 

 membrana tympani with a sharp well-defined border. One of the semicircular canals forms 

 the tumid border circumscribing the fossa for the cerebellar appendage. At the back part of 

 the middle section is shown the horizontal septum dividing the upper from the lower tympanic 

 cell : the~ venous sinus is exposed in the fissure between the tympanic and squamosal. At 

 the fore part of the middle section the rhinencephalic chamber is seen, bounded below and 

 laterally by the commencement of the olfactory chamber : the anterior termination of the 

 rhinencephalic chamber is seen in the anterior section. 



Presented by Prof. Owen, F.K.S. 



The following are parts of the same skeleton of an Agouti (Dasyprocta Agvti) : 



Hunterian. 



2052. The cranium. 



The calvarium is removed. The sella turcica is shallow, and not defined by clinoid pro- 

 cesses ; the chiasmal platform is subquadrate, and leads to a fossa, perforated by the two 



