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IX. On the Structure and Bemlojjmeni of tlu-: Skull m the Pig (Sus scrofa). 



JBy W. K. Parksk, 



Received May 1 7, — Read June 19, 1873. 



My intention for some time past has been to follow up the Morphology of the Fish's 

 skull by that of the Mammal; and as amongst the " Placentalia " the Guineapig (Cavia 

 aperea) takes a very low place, it was chosen as the type to work out. I have been led 

 to change my plan, however, and to take a medium type by an unexpected supply of 

 materials kindly put into my hands, in November 1871, by my friend Mr. Charles 

 Steavart ; these were about seventy embryos of the Common Pig, a considerable number 

 of which were barely two thirds of an inch in length, whilst others measured 6 inches 

 in a straight line from the snout to the tuberosity of the ischium *. 



As the tissues in the earlier stages were only in a nascent condition, the greatest care 

 has been taken to harden them for slicing into sections and for dissection from without 

 inwards ; and no labour has been spared in this matter the sections being made after 

 the hardened embryos had been imbedded in solid paraffin. These extremely thin objects 

 were coloured with an ammoniacal solution of carmine, and then transferred to slides, 

 on which they were mounted in acid glycerine. The coarser sections of the larger 

 embryos, to be used as opaque objects, were made without imbedding, after the specimens 

 had been immersed in a dilute solution of nitric or muriatic acid, to which had been 

 added some chromic acidf; in the former way I have been able to obtain views of the 

 tissues of the earliest stage under a magnifying-power of as much as 600 diameters, 

 although about 50 diameters has been found to be the most useful, showing, as such a 

 lesser enlargement does, the various parts in relation to each other, and enabling the eye to 

 follow the granular thickenings which are becoming differentiated into special tissues. 



The study of this particular type of Mammalian skull has been facilitated by prepa- 

 ratory work in many other types of this Class, extending over a period of thirty-three 

 years ; but I have determined not to bring any thing forward relating to special modifi- 

 cations until this more exhaustive piece of work has seen the light. 



The first impulse in this direction was given me by an invaluable work which appeared 

 long ago; I refer to W. Cheselden's 'Anatomy of the Human Body' (London, 1722, 

 8vo). But my newer stand-point is from the ' Elements of Comparative Anatomy' 

 (1864), by Professor Huxley (Lecture 7th to the end). 



* The actual length of these embryos, measured along the curved line of the spine to the end of the tail, is 

 about one half more than is given by my practical and easier method of admeasurement. 



t All the finer sections and preparations were made by my son, Mr. T. J. Parker. 

 MDCCCLXXIV. 2 Q 



