No. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORT MAN. 47 



in certain cases whether given resemblances represent real genetic 

 affinities or are mere convergences. How much more likely that thi& 

 should have happened where the result was dependent upon a single 

 or a few primary factors, like the enlargement of the brain and the 

 functional development of the teeth. Altogether I am disposed to 

 look upon the polyphyletic origin of the Mammalia as not at all 

 improbable. 



T?ie temporal area. — In the primitive reptilian skull the temporal 

 area is completely covered over with a bony roof (tegmen temporalis) ,. 

 freely communicating in front with the orbital cavity and having a 

 large opening behind on each side and above the foramen magnum, 

 the supraoccipital vacuity. In the recent state this latter opening 

 is largely occupied by the powerful neck muscles which are attached 

 to the skull in this region, just as the space under the bony roof and 

 between it and the brain case is occupied by the temporal and ptery- 

 goid muscles. Upon the outside and below the supraoccipital 

 vacuity is a second opening jTiercing the quadrate from before back- 

 wards, whose boundaries may be furnished by the quadrate alone^ 

 or in conjunction with quadra to-jugal. As the upper vacuity is 

 called the supraoccipital so the lower should be termed the lateral 

 occipital or quadrate vacuity. 



In different orders of the Reptilia this bony roof loses its conti- 

 nuity and is interrupted by one or two openings called, respectively,, 

 the supreitem.poral vacuity and the latered temporal vacuity ^ the various- 

 arrangements of which furnish some important characters for the- 

 classification of the major divisions. As a result, therefore, of the 

 appearance of these vacuities, the tegmen temporalis is broken up into 

 the various arches or arcades which furnish the boundaries of these 

 openings. Thus we have in such a typically reptilian skull as that of 

 5'p/V?iocZo/i (fig. 15)a temporo-occipital arch or arcade which occu- 

 pies the position of the lambdoidal crest of the mammal, above and ta 

 the outside of the occipit, and separates the supraoccipital vacuity 

 behind from the supratemporal opening in front. We likewise have a 

 supratemporal arcade running backwards from the postorbital arch^ 

 cutting off the supratemporal vacuity from the lateral temporal 

 opening and lastly the postorbital arch limiting the orbit behind and 

 the quadrato-jugal arch completing the boundary of the eye cavity 

 and the lateral temporal vacuitj^ below. 



It has been already noticed on a former page how in the transition 

 from the reptilian or batrachian to the mammalian condition, because 

 of the great enlargement of the brain case many of these arches and 

 vacuities have either been obliterated or profoundly modified, most 

 probably as a direct result of muscular pressure; and it now remains 

 to discuss the possible or probable types of reptilian or batrachian 

 skull from which some of the various types of mammalian skulla 



