ox TIIK AUDITORY REGION' IN DICYNODON. 419 



Pl. LIV. 



Fig-. 20. Hlood ot'ii Palm Tanager sliowiiiij infection with Hfeiiinprofeus (hoithirnliifi. 

 Tliict! f'ull-sizt'il parasites are ])resent, and some eHrl3' forms are seen in 

 tlie iili()ton;ra|ili as dots in the erytlirocvtes. 



Fig'. '21. Hlood of a llenpil Monitor sliowiii;;; an or<linary lucmosfrep^avine and the one 

 mentioned on p. ■112 of text. X 4oO. This is prolialdy a double infection 

 as no intermediate stages between these parasites can be seen. 



At <( the ordinaiy form ot Inemogregarine is seen ; those ei-ythrocytes 

 marked h contain the new type of parasite, to whicli reference has Iteen 

 made in the text. This ])ara8ite stains badly, there is a very small 

 amount of nuclear material in it when staineii by any modification of 

 the Komanowsky method or by iron-logwood, and the altered nucleus of 

 the erythrocyte stains very <lensely. 



Fig. 22. Drawings of the same parasites. At a tlie ordinary liaMnogregarines are 

 shown, and at h the other parasite, in aij early stage in the drawing to 

 the left, and in the later stage, with the cell-nucleus divided, to the 

 right. 



Pl, LV. 



Fig. 23. Drawings of the new parasite. 



The erythrocyte in the photograph and drawings is seen to be deformed, 

 and eventually delia-moglobinised (as in the cell marked a). At h is 

 seen the tiny nodule which is generally to be found on the delicate con- 

 necting-thread between the piece.s of the cell-nncleus. 'J'lie cell marked 

 c contains what appears to be an abortive attempt to divide the cell- 

 nucleus equally : very few of the.se were found. 



F'ig. 24.. Drawings of forms found in the lungs, showing various stages in schizogony. 

 None of these snnil! forms have been found in the erythrocytes. Ko 

 stages were found in the other organs. 



23. On the Structure of tlie Internal Ear and the 

 Helations of the Ba.'^icranial Nerve.s in J>iri/nod(m, and 

 on the Honiolojiv of the Maninialinu Auditory 0.s.sicles. 

 By J{. Broom, M.D., D.Sc, C.M.Z.S. 



[Received January 12, 1912: Read March 5, 1912.] 

 (Plate LVI.* and Text-figure 53.) 



Few questions connected with vertebrate morphology have 

 given rise to a larger amount of discussion than the homology 

 of the mammalian auditory ossicles and the connected problem 

 of the fate of the quadrate in mammals. Most embryologists 

 have been struck with the resemblance of the malleus and incus 

 to an articular and quadrate ; many comparative anatondsts have 

 been impressed rather with the resemblance of tlie mammalian 

 auditory chain with the auditory apparatus of the Reptilia ; 

 while palaeontologists, for the most part, have heisitated to 

 believe that the incus could be the quadrate, from the ditficultv 

 of imagiidng the intermediate stages, and have inclined rather to 

 believe that the quadiate has become part of the zvgomatic arch, 

 or the meniscus, or become lost, or converted into the tympanic 

 bone. 



Until a few months ago I was of opinion that the quadrate 

 became either the meniscus or, in those few forms where a meniscus 

 is absent, was lost. It is unnecessary to repeat the arguments 



* For explanation of the Plate see p. 125. 



