CON T ENTS 
OF VOI,. 160. 
I. Note on Professor Sylvester’s representation of the Motion of a free rigid Body by 
that of a material Ellipsoid whose centre is fixed , and which rolls on a ro ugh Plane. 
By the Rev. N. M. Ferrers, Fellow and Tutor of Gonville and Gains College , 
Cambridge. Communicated by Professor J. J. Sylvester, F.R.S. . . page 1 
II. On the Refraction-Equivatents of the Elements. By J. H. Gladstone, Ph.D., 
F.R.S 9 
III. Magnetic Survey of the. West of France, 1868. By the Rev . Stephen J. Perry, S.J. , 
F.R.A.S. , F.M.S. , 8fc. Communicated by the President 33 
IV. A Memoir on Abstract Geometry. By Professor Cayley, F.R.S 51 
V. On Remains of a large extinct Lama (Palauchenia magna, Ow.) from Quaternary 
Deposits in the Valley of Mexico. By Professor Owen, F.R.S. Ac. . . . 65 
VI. On the Molar Teeth , Lower Jaw , of Macrauchenia patachonica, Ow. By Professor 
Owen, F.R.S. &c 79 
VII. On a Group of Varieties of the Muscles of the Human Neck , Shoulder , and Chest , 
with their transitional Forms and Homologies in the Mammalia. By John Wood, 
F.R.C.S . , Examiner in Anatomy at the University of London. With three Plates 
of illustrations and explanations. Communicated by Hr. Sitarpey, Sec.R.S. 83 
VIII. An Inquiry into the Variations of the Human Skull, particularly in the Antero- 
posterior Direction. By John Cleland, M.D., Professor of Anatomy and Physio- 
logy, Queen's College, Galway. Communicated by Dr. Allen Thomson, F.R.S. 117 
IX. On the Proof of the Law of Errors of Observations. By Morgan W. Crofton, 
F.R.S 175 
X. On the Mineral Constituents of Meteorites. By Nevil Story-Mas kelyn e, M.A., 
Professor of Mineralogy, Oxford, and Keeper of the Mineral Department , British 
Museum. Communicated by Professor II. J. Stephen Smith, F.R.S. . . 189 
