244 
ZOOLOGY: E. P. ALUS 
In the Amphibia the basis cranii apparently corresponds to the roof, and 
not the floor, of the dorsal myodomic cavity of Amia and the Teleostei. The 
fenestra hypophyseos of these animals is, then, the homologue of the pituitary 
opening of the brain case of fishes. 
In the Reptilia and Mammalia a dorsa 1 myodomic cavity s found that is 
similar to that in Ceratodus. In man it is represented in the cavernous and 
intercavernous sinuses, and the venous vessels that traverse those sinuses are 
the homologues of the pituitary veins of fishes. 
The cartilago acrochordalis of Sonies's 2 and Noordenbos's 3 descriptions of 
birds and mammals, respectively, is the homologue of the cartilaginous pro- 
otic bridge of embryos of fishes. The open space between this cartilage, or 
bridge, and the anterior end of the parachordal plate is the fenestra basicran- 
ialis posterior properly so called. This fenestra is a perforation of the roof of 
the myodomic cavity, and hence is not the homologue of the so-called fenestra 
basicranialis posterior of embryos of fishes, which fenestra is a perforation of 
the floor of that cavity. This latter fenestra of embryos of fisjies is the homo- 
logue of the fenestra hypophyseos of birds and mammals, the so-called anterior 
prolongations of the parachordals of fishes being the homologues of the polar 
cartilages of birds and mammals. 
In certain of the Selachii there is an acustico-trigemino-facialis recess, and 
there may be certain canals in the cranial wall that are traversed by the vena 
jugularis and the external carotid artery. 
In Amia the trigemino-facialis portion of this recess has fused with the 
canals for the vena jugularis and the external carotid artery to form a tri- 
gemino-facialis chamber, this chamber has become continuous ventrally with 
the myodome, and the large chamber so formed has been prolonged anteriorly 
by a space enclosed between the pedicel of the alisphenoid and the primitive 
side wall of the neurocranium. The foramina for the pituitary vein and the 
nervi oculomotorius and trochlears open into this anterior prolongation of 
the chamber, and, through its orbital opening, into the orbit. The vena jugu- 
laris traverses this orbital opening to enter and traverse the trigemino-facialis 
chamber; the musculus rectus externus traverses it to enter the myodome; 
and the nervus profundus traverses it to join the ganglion or root of the nervus 
trigeminus. The nervus trigeminus and the external carotid artery issue from 
the trigemino-facialis chamber posterior to the pedicel of the alisphenoid and 
run forward lateral to it. 
In the non-siluroid Teleostei the trigemino-facialis chamber is not continu- 
ous with the myodome, and it has been separated by a wall of bone into partes 
ganglionaris and jugularis that correspond, respectively, to the trigemino- 
facialis recess and the jugular and external carotid canals of the Selachii. 
The pedicel of the alisphenoid is incomplete, or wholly wanting, but it may 
be replaced by an anterior prolongation of the ascending process of the para- 
