320 THROUGH THE HEART OF PATAGONIA 



two posterior molars slightly different in shape from those of the former 

 mandible. In this specimen the longer axis of the third molar is oblique, 

 whereas in No. 9 it is coincident with the axis of the mandible ; while in 

 the former the fourth molar is not so long in proportion to its width as in 

 the latter. Such slight differences, however, cannot be regarded in the 

 Edentata as more than individual variations. 



Brain-cavity and Cerebral Nerves. 



By the kind permission of Dr. Moreno, the cranium No. i has 

 been vertically bisected to display the character of the cranial cavity 

 and the nerve-foramina. An instructive plaster-cast of the cavity 

 has thus been made by Mr. C. Barlow, the Formatore of the British 

 Museum. 



The olfactory lobes are shown to have been well developed, pro- 

 jecting a little in front of the cerebral hemispheres. These hemi- 

 spheres are together somewhat longer than broad, slightly broader behind 

 than in front, and a little constricted in the middle. They do not over- 

 lap the cerebellum, which is relatively large. The origins of the nerves 

 are very imperfectly shown in the cast ; only their exits from the cranial 

 cavity are clear. The most interesting are the optic and trigeminal nerves, 

 which pass out of the cranial cavity at first by a common exit, which is 

 soon subdivided by a bony partition into two canals, the former no less 

 than 0.08 m., the latter 0.045 m- in length. The fourth, seventh, eighth 

 and twelfth nerves are also recognisable on the cast ; and one prominence 

 of plaster has filled the foramen lacerum posterius. 



Compared with the brains of Mylodon and Scelidotherium, so far as 

 known from casts of the cranial cavity,* that of GrypotJurium is observed 

 to be more elongated, with less divergent and prominent olfactory lobes, 

 less constricted cerebral hemispheres, and a larger cerebellum. In the 

 form and proportions of the cerebrum and cerebellum, it similarly differs 

 from Megatherium.^ The cerebral hemispheres of the existing Choloepus 

 didactylus and Bradypus tridactylus\ are more tapering forward, and their 

 cerebellum is relatively smaller than in Grypotherium. 



■■■■ P. Gervais, " Memoire sur les Formes Cerfebrales propres aux Edentfis vivants et 

 fossiles," Nouv. Arch. Mus., vol. xv. (1869), p. 39, pi. iv. Figs, i, 2. 

 i' P. Gervais, loc. cit. p. 39, pi. v. 

 I Ibid. p. 38, pi. iv. Figs. 3, 4. 



