260 DK. c. I. roESYTH 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 

 bv the frontal, the anterior prolongation of the orbital process is 

 large (Microcebus occupies an intermediate position between the 

 Malagasy and non-Malagasy Lemurs) (text-tigs. 65, 66, p. 25'*). 

 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 by the frontal, another con- 

 tributing 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 iVifm, the orbital process of the palatal is more or less hollow 

 and completes, so to say, one of the ethmoidal cells, by closing it. 

 In very exceptional cases (M. J. Weber) this cavity of the human 

 palatal opens into the maxillary sinus. 



The palatal of Man 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 Eertini) ; 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 " '-. 



Henle holds that part of the processus orbital is. ^ helps to close 

 the sinus sphenoidalis when its wall is incomplete ^ 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). 

 - Op. cit. p. 297. 



3 " Was von der Grundflaohe des Proc. orbitalis hinter seiner Oifnuug iibrig 

 bleibt, legt sich vor die Jatei-ale untere Ecke der vorderen Wand des Wespeu- 

 beinkorpers und tragt, wenn diese Wand unvollstandig ist, zur Schliessung der 

 Wespenbeinhohle bei." (Handb. d. syst. Anat., 3rd ed., I. i. p. 190, 1871.J 



*■ Lotos, Jahrb. f. Naturwiss., N.F. iii. & iv. p. 75 (1833). 



