118 



MR. E. PHELPS ALLIS, JUX., ON 



examined, dorsal to the trabecule, and where there is a sub- 

 orbital shell" it lies dorsal to that shelf. This foramen of 

 Chimcera, which is quite unquestionably the homologue of the 

 foramen in the Selachii, must then have become surrounded by 

 and quite deeply enclosed in the dorso-lateral edge of the 

 trabecula, the membranous lateral wall of this part of the neuro- 

 cranium thus lying lateral to it and the foramen appearing to lie 

 in the floor of the cranial cavity. The foramen is not shown 

 in Daan's figure of an embryo of Chimcera, doubtless because 

 it is hidden, in dorsal view, by the supraorbital portion of the 

 cranial wall. 



The branch of the pseudobranchial artery that accompanies 

 the nervus opticus to the eyeball was called by me, in the earlier 

 work just above referred to, the arteria ophthalmica magna, this 

 identification of the artery being based on its apparent origin, in 

 a dissection in which the tissues had evidently been torn, from 

 the pseudobranchial artery before that artery enters the cranial 

 cavity. This is, however, an error, the artery quite certainly 

 being the arteria centralis retime, or optic artery, of my descrip- 

 tions of the Selachii, and no arteria ophthalmica magna being 

 found in this fish. 



At the hind end of the orbit five foramina, lying close together, 

 perforate the cranial wall and transmit the nervi profundus, 

 trigeminus, buccalis lateralis, facialis, and abducens. The fora- 

 men for the facialis is always separated from the other foramina 

 by cartilage, and the foramen for the abducens usually so 

 separated, the other three nerves usually issuing through a single 

 foramen but being separated from each other by membrane. 

 Dorsal to these foramina there is a large foramen for the ramus 

 ophthalmicus superticialis *, and two foramina that lie near the 

 edge of the membranous mesial wall of the orbit, one of them 

 transmitting the nervus trochlearis and the other a venous vessel 

 which is doubtless the anterior cerebral vein of my descriptions 

 of Amia and the Teleostei. Slightly anterior to the five foramina 

 that transmit the trigeminus, facialis, and abducens nerves there 

 is the foramen for the nervus oculomotorius, which lies at the 

 edge of the membranous mesial wall of the orbit, and ventro- 

 lateral to that foramen there is a small foramen for the pituitary 

 vein, this latter foramen opening into the pituitary fossa. The 

 vein that traverses this latter foramen is small, and although it 

 connects with *its fellow of the opposite side in the usual piscine 

 manner, it is always in communication with a vein that issues 

 from the cranial cavity through the foramen for the nervus 

 vagus. There is in this fish no transverse pituitary canal such 

 as is found in many of the Selachii. 



Lateral to the several foramina above described, there is a 

 large perforation of the suborbital shelf which transmits the 

 ramus hyoideo-mandibularis facialis and the vena jugularis, and 

 anterior to that foramen there is another perforation of the 



* A small foramen is, by error, shown in figure 3, Piute II., lying slightly ventral 

 to this large foramen. It <loes not east in the fish. 



