172 



GREGORY: NOTHARC'TUS, AN AMERICAN EOCENE PRIMATE 



forward in a groove in the roof of the tympanic cavity issuing into the temporal fossa (van Kampen, 

 p. 430) through a notch or foramen (which may be named foramen caroticum ahsphenoidei, /. c. al.) 

 in the tympanic process of the aUsphenoid, posteroexternal to the foramen ovale; this branch of the art. 

 stapedia constitutes the ramus inferior ("art. maxillaris interna Calori," Winge). After leaving the 

 tympanic fossa the ramus inferior passes forward medial to the foramen ovale and enters a very short 



Fig. 1 



64. Semidiagrammatic representation of the left tympanic region of a primitive mammal, after the removal of 



the ossicles and tympanic membrane. After Van Kampen. 



a.t. 



.innulus tympanicus. 



pr. 



promontorium (cochlea). 



c.i. 



carotis interna ("art. promontorii"). 



aM. 



"arteria stapedia," passing across the fenestra ovalis (stapes omitted) and then running forward to divide into the ramus 





superior and ramus inferior {r.i.). 



f.o. 



foramen ovale. 



f.l.m. 



foramen lacerum medium. 



f.l.p. 



foramen lacerum posterius. 



cl. 



chorda tympani. 



/. 



nervus facialis. 



r.e. 



recessus epitympanicus ("attic") (ossicles removed). 





apertura canalis facialis. 



h. 



tympanohyal. 





processus mastoideus. 



p.p.l. 



])rocessus post-tympanicus. 



p.p.g. 



jirocessus postglenoideus. 



J-'J- 



foramen postglenoideum. 



t.t. 



tegmen tympani. 



M. 



cartilago Meckelii. 



i.a. 



tuba auditiva (Eustachii). 



The fenestra cochleae (rotunda) lies beneath the posterior part of the annulus (a. t.). 



alisphenoid canal ("canalis pterygoideus") on the outer side of the pterygoid plate of the alisphenoid; 

 in front of this alisphenoid canal the ramus inferior gives rise to the large art. temporalis profunda, the 

 ramus orbitalis and other branches. 



The second branch of the art. stapedia, called the ramus superior, springs from the main branch in 

 the anterior part of the tympanic fossa, at a point about three millimeters medial to the postglenoid 

 foramen. The ramus superior passes backward and upward, traversing the anterior margin of the petrosal, 

 bending outward and issuing into the mid-cranial fossa near the outer angle; turning forward it gives off 

 a small middle meningeal branch, and following the cerebral surface of the temporal it makes its exit 

 into the orbit, through the cranio-orbital foramen where it anastomizes with the ophthalmic and ramus 

 orbitalis [Tandler]. 



The arteria promontorii, as in Lemur, is given off from the common stem of the entocarotid near the 



