726 B. W. KUNKEL 



being supported ventrally by the septum interorbitale which 

 increases rapidly in height from its posterior end. The lateral 

 margin as it passes over into the pila metoptica is incised by the 

 broad sinus oculomotorius for the oculomotor nerve as it passes 

 obliquely to the outside of the cranium through the fenestra 

 metoptica. Near the anterior margin, the subiculum infundibuli 

 is perforated by a pair of large oval foramina (foramen ophthal- 

 micum, f.o., fig. 25) through which the arteria ophthalmica 

 passes to reach the orbit. In the embryo modelled there is a 

 small fenestra on the right side only which represents the first 

 step in the resorption of this part of the chondrocranium. The 

 subiculum infundibuh is much thicker anteriorly and laterally 

 than medially and behind, and in older embryos in which the 

 resorption has been carried farther, the entire posterior part of 

 the subiculum has disappeared and the foramen ophthalmicum 

 becomes a sinus, opening freely behind into the fenestra metop- 

 tica. In older embryos the interorbital septum becomes fenes- 

 trated by a long, narrow opening which extends both anterior 

 and posterior to the subiculum infundibuli, its anterior end lying 

 beneath the fenestra optica, so that, as in Lacerta, a cartilago 

 hypochiasmatica is differentiated. 



The pila metoptica is a short, stout rod extending antero-later- 

 ally from the antero-lateral angles of the subiculum infundibuli 

 to the posterior margin of the planum supraseptale. The nervus 

 oculomotorius passes ventral to the pila metoptica, leaving the 

 cranial cavity through the sulcus oculomotorius. The nervus 

 trochlearis passes out of the cranial cavity through the fenestra 

 metoptica lateral and dorsal to the nervus oculomotorius, lying 

 parallel to the latter beneath the pila metoptica. 



The fenestra prootica is a large, oval opening between the ante- 

 rior cupula of the otic capsule and the prefacial commissure behind 

 and the pila prootica in front. On account of the curved form of 

 the latter the fenestra is enclosed by it dorsally as well; the 

 closure, however, is not complete on account of the absence of a 

 taenia marginalis and the failure of the pila prootica to fuse with 

 the otic capsule, a condition which resembles Sphenodon. The 

 fenestra is completely filled by the large gangUon semilunare 



