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Show Z W DR. C. I. FORSYTH MAJOR ON [Mar. 19, With regard to the Oriental and Ethiopian Lemurs, all of which, as stated, have a well-developed planum and in all of which the orbital process of the palatal is small, I submit, pending a more accurate investigation, that this process belongs to the palatal exclusively. In the Malagasy Lemurs, in which part of the planum is shielded by the frontal, the anterior prolongation of the orbital process is large (Microcebus occupies an intermediate position between the Malagasy and non-Malagasy Lemurs) (text-figs. 65, 66, p. 258). For the reasons stated above, I have submitted, that in this group the larger portion of the orbital process is in reality a part of the planum, which, in union with a small portion of the palatal, helps to form the walls of a pneumatic cavity. There are cases, however- Hapalolemur and sometimes Lepidolemur (text-figs. 67, 68, p. 259) -in which occurs besides a separate bone, which, from its position, has the claim of being a small independent portion of the planum. So that in these exceptional cases the planum is represented by three distinct portions-one covered hy the frontal, another contributing towards the formation of a sinus, and a third, which plays the usual part of a planum, but is greatly reduced in size. This last can scarcely be regarded as a stop-gap, an intercalar bone, for in the case of Hapalolemur at least it is already present in a new-born specimen. In Man, the orbital process of the palatal is more or less hollow and completes, so to say, one of the ethmoidal cells, by closiug if. In very exceptional cases (M. J. Weber) this cavity of the human palatal opens into the maxillary sinus. The palatal of M a n is, according to the general assumption, developed from a single osseous centre. But Cleland has drawn attention to the circumstance ' that, not uncommonly in Man, the orbital process is unusually large, owing, he believes, to its having incorporated one of the three elements of the sphenoidal spongy bones (ossicula Bertini); for it has the same position which is occupied by that element when it appears in the orbit, and the enlarged orbital process replaces the element by contributing towards the formation of the lateral wall of the cavity (sinus sphe-noidalis) which owes its origin to the spongy bones. In three young Orang skulls Cleland found that " the sphenoidal spongy bones take part in the formation of the orbit, while the palatal has no orbital plate " 2. Henle holds that part of the processus orbitalis helps to close the sinus sphenoidalis when its wall is incomplete 3. A similar view is advocated by Toldt ', who says that when the spongy bones are rudimentary, the orbital process may contribute in a comparatively 1 Phil. Trans. Roy. Soc. London, vol. 152, pp. 291, 292 (1862). 2 Op. cit. p. 297. 3 " W a s von der Grundflache des Proc. orbitalis hinter seiner Offnung iibrig bleibt, legt sich vor die laterale untere Ecke der vorderen Wand des Wespen-beinkorpers und tragt, wenn diese W a n d unvollstiindig ist, zur Schliessung der Wesuenbeinhohle bei." (Handb. d. syst. Anat., 3rd ed., I. i. p. 190, 1871.) 4 Lotos, Jahrb. f. Naturwiss., N.F. iii. & iv. p. 75 (1833). |