bo 
MYODOME AND TRIGEMINO-FACIALIS CHAMBER res, 
CHONDROSTEI 
The descriptions that I find of the pituitary region of the 
cranium of the Chondrostei are incomplete, and but little can be 
said about it. A slight pituitary fossa is:sshown by Bridge (’79) in 
the chondrocranium of Polyodon, and both I (711) and Dan- 
forth (12) have described the arteries in this fish. In embryos 
of from 150-mm. to 170-mm. in length the internal carotid runs 
forward along the ventral surface of the neurocranium, at first 
ventral to a short lateral process of the parasphenoid, and then, 
anterior to that process, in a groove on the ventral surface of 
the lateral edge of the basis cranii, lateral to the lateral edge 
of the parasphenoid. The artery there becomes enclosed in 
dense fibrous tissues which are attached to the cranial wall, 
and while in the canal thus formed, it is joined by the nervus 
palatinus facialis, which issues from the cranial cavity through 
a special perforation of the cranial wall. The internal carotid 
then enters a canal in the cranial wall, receiving while in it, 
the efferent pseudobranchial artery, and then immediately 
gives off the arteria ophthalmica magna. <A small pituary vein 
is sent outward from the pituitary fossa, through a special 
foramen in the cranial wall, and falls into the vena jugularis. 
The nervus abducens traverses a short canal in the cartilage 
of the basis cranil and, issuing from it, apparently again lies 
in the cavum cerebrale crani, from which it definitely issues 
with the main root of the nervus trigeminus. 
There is thus evidently, in Polyodon, a subpituitary space 
corresponding to the myodomic cavity of Amia, but the con- 
ditions need further investigation. The ventral compartment 
of the teleostean myodome is represented in the canal of fibrous 
tissue traversed by the internal carotid artery and the nervus 
palatinus facialis, this apparently corresponding to the canal 
through the ascending process of the parasphenoid of Polypterus. 
