724 B. W. KUNKEL 



The pila prootica which forms the lateral portion of the tem- 

 poral region may be described in general as a broad U-shaped 

 plate of nearly uniform width, with, its convex side anterior and 

 its concave side posterior, and exhibiting accordingly a median 

 and a lateral limb. It is attached to the basal plate by the median 

 limb, wliile the external limb of the U is somewhat dorsal to the 

 former and ends freely close to and medial to the anterior cupula 

 of the otic capsule. The plane of the whole plate is so curved 

 that while it is nearly horizontal in a transverse direction at its 

 attachment to the basal plate, the free lateral limb is nearly verti- 

 cal in its position. The median limb is inclined antero-dorsally 

 from its proximal end where it is attached to the front surface of 

 the crista sellaris. The lateral Umb of the pila exhibits a small, 

 anteriorly directed process which approaches a posteriorly directed 

 process from the postero-lateral angle of the planum supraseptale. 

 These two processes narrow the fenestra metoptica dorso-later- 

 ally without closing it in completely, and suggest, in their posi- 

 tion, an incomplete taenia marginalis. In another embryo, 

 slightly younger than that modelled, this anteriorly directed 

 process of the lateral limb is greatly enlarged and is perforated 

 by a large foramen, the significance of which is still undetermined. 



In the embryo modelled, the pila prootica grows very thin 

 toward its dorso-lateral margin and passes gradually into a thin 

 layer of dense connective tissue which extends dorsally and medi- 

 ally and encloses the cranial cavity above. 



A peculiarity of the individual modelled, which has not been 

 met with in any of the other specimens studied, is the presence 

 of a short cyUndrical rod-Uke process from the dorsal surface of 

 the medial limb of the pila prootica near its distal end which 

 extends postero-laterally in a horizontal plane and ends freely in 

 the cranial cavity medial to the anterior margin of the fenestra 

 prootica. The nervus oculomotorius, as it passes anteriorly 

 over the medio-dorsal sm-face of the pila prootica in order to leave 

 the cranial cavity tlu-ough the fenestra metoptica, lies dorsal and 

 medial to this process, while the n. trochlearis, which is approxi- 

 mately parallel to the oculomotor, lies lateral and dorsal to this 

 same process. Beneath the pila prootica, running horizontally 



