Cope.] [March 16, 1877. very large olfactory lobes in front. Cerebellum very small and flat; middle brain large. This character is sustained by that of the ankle joint, which, existing in two such distinct divisions as the Amblypoda and Creodonta, may be found to characterize the entire sub-class, but this is not yet certain; it is as follows: Tibio-astragalar articulation flat, and without groove or segment of pulley. This sub class stands below the Lyencephala in its position, approximating the reptiles in the points above mentioned, more nearly than the latter do. It includes two orders, one ungulate, the Amblypoda, the other unguiculate, the Bunotheria.* To the former belong the sub-orders Pantodonta and Dinocerata; to the latter the Creodonta and probably the Tillodonta and Taniodonta. Whether the Mesodonta belong to it is not certainly ascertained, while the Insectivora do not belong to it, as they are rightly placed in the sub class Lissencephala. Lartet first pointed out the fact of the successive increase in the size of the brain of the Mammalia with the advance of Geologic time; and Marsh has stated that this increase is to be observed principally in the relative size of the cerebral hemispheres. I would correct the latter statement so far as to add, that the increase of size is to be seen in the cerebellum as much as in the hemisphere. It is also evident that the relative decrease is in the middle-brain and olfactory lobes. Explanation of Plates. Pl. I. Cast of brain cavity of Coryphodon elephantopus, two-thirds the natural size. The right bulbus of the olfactory lobe is probably too large above, owing to the want of preservation of the superior wall of the cavity. Fig. 1. Superior view; fig. 2, the left side; t. base of the trigeminus nerve. Pl. II. The same. Fig. 1, from below; fig. 2, posterior; fig. 3, anterior views. t. base of the trigeminus nerve; md. base of the mandibular branch of the trigeminus; p, ribs continuous with anterior pyramids. See Proceedings Academy Natural Sciences of Philadelphia, 1876, p. 88. |