1900.] GRYPOTHEBIUM (nBOMTLODON) LISTAI. 69 



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. 1 has 

 been vertically bisected to display the character of the cranial 

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

 cavity (shown of one-hall; the natural size in PL VII.) has thus 

 been made by Mr. C. Barlow, the Porinatore of the British Museum. 



The olfactory lobes (ol.) are shown to have been well-developed, 

 projecting a little in front of the cerebral hemispheres (c). These 

 hemispheres are together somewhat longer than broad, slightly 

 broader behind than in front, and a little constricted in the middle. 

 They do not overlap the cerebellum (cb.), which is relatively 

 large. The origins of the nerves (fig. 1 b) are very imperfectly 

 shown in the cast ; only their exits from the cranial cavity are 

 clear. The most interesting are the optic (II.) and trigeminal 

 (V.) 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 (IV.), seventh (VII.), eighth (VIII.), and 

 twelfth (XII.) nerves are also recognizable on the cast ; and one 

 prominence of plaster (/.) has filled the foramen lacerum posterius. 



Compared with the brains of Mylodon and SceUdotherium, so far 

 as known from casts of the cranial cavity \ that of Grypotherium 

 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 2 . 

 The cerebral hemispheres of the existing Cholcepus didactylus and 

 Bradypus tridactylus 3 are more tapering forward, and their 

 cerebellum is relatively smaller than in Grypotherium. 



Auditory Ossicles. 



The auditory ossicles were preserved in the tympanic cavities of 

 both skulls, nos. 1 and 2, being retained by the dried soft parts. 

 They were detected by Prof. Charles Stewart, who kindly extracted 

 them, with great skill, from both sides of each skull. The series of 

 the right side of the first specimen is shown of twice the natural size 

 in the drawing(Pl. VI. fig. 4). Comparing these ossicles with the fine 

 collection in the Koyal College of Surgeons, they prove to be closely 

 similar to those of all the existing Sloths, but most nearly resembling 

 those of Gholospus didactylus. The malleus (m.) is bent exactly 

 as in the latter species, and is of similar shape. As observed by 

 Prof. Stewart, it is remarkable in ai'ticulating with the incus not 



1 P. Gervais, " Memoire sur les Formes Cerebrales propres aux Edentes 

 vivants et fossiles," Nouv. Arch. Mus. vol. xv. (1869), p. 39, pi. iv. figs. 1, 2. 



2 P. Gervais, he. cit. p. 39, pi. v. 



a P. Gervais, loc. cit, p. 38, pi. iv. figs. 3. 1. 



