SINUS PARANASALES 



While not an integral part of the brain, yet the frontal and facial sinuses are interesting in 

 connection with it. There are several skulls of different genera in the Marsh Collection which, 

 collectively, show these sinuses. However, the general pattern is the same in all of them, and 

 Moodie (1916, pp. 137-141) has so well described the structure of Merycochoerus that I shall quote 

 from his work (Figs. 187-188). 



The elongate maxillary sinus has a most unusual posterior extent, and there are no sacculations 

 of the frontal sinus, such as are seen in the pig and ox, although the diploe were considerably 

 enlarged. 



Sin sag. 



Sin. 



Fig. 188. — Merycochoerus. — Superior view of endocranial and sinus paranasales cast. C. n., nasal cavity; Lb. s., lobulus 

 simplex of cerebellum; S. cor., coronary sulcus; S. Int., lateral sulcus; S. n., nasal septum; S. ss., suprasylvian sulcus; 

 Sin. /., frontal air sinus; Sin. i. lat., inferolateral blood sinus; Sin. max., maxillary air sinus; Sin. max. sup., superior maxillary 

 air sinus; Sin. sag., superior sagittal blood sinus. About 1/2 nat. size. (After Moodie, 1922.) 



Moodie found that the sinuses in this merycoidodont more nearly resembled those of the sheep 

 than those of the pig. He further describes them as follows: 



The group of small (separate) cavities just anterior to the brain, are, doubtless, all divisions of the frontal 

 sinus. . . . None of the cavities in the fossil seem to be due to infoldings of the ethmoturbinal, but are either 

 divisions of the frontal or maxillary sinuses. The smaller posterior, or frontal sinuses, are separated from each 

 other by rather thick partitions of bone (aire ossi frontali). It is quite evident that the large cavities just anterior to 

 the small posterior ones, are sacculations of the maxillary sinus, which have been named the sinus maxillaris 

 superior, as in the sheep and horse. The relatively great distance, thirty millimeters, between the most anterior one 

 of the sinus maxillaris superior and the base of the sinus maxillaris inferior is traversed by a canal which is possibly 

 homologous to the ostium maxillare. This condition is particularly parallel in the sheep, but whether it is proper 

 to speak of this opening as the ostium maxillare, or not, is uncertain. 



