736 
MR. A. SANDERS ON THE ANATOMY OF THE 
may be considered as an appendage to the thalamencephalon ; they are not so well 
developed, comparatively speaking, as in the Teleostei. In front of them is seen the 
chiasma nervorum opticorum, while at their posterior end in the furrow between them 
and the anterior end of the medulla oblongata is situated the hypophysis cerebri or 
jhtuitary body ; this is connected with the inferior end of the infundibulum by a 
glandular tube. On each side of the hypophysis cerebri is a membranous vesicle, the 
saccus vasculosus, which differs from the part with the same name in the Teleostei in 
not being glandular. The saccus vasculosus of the Teleostei is probably included in the 
pituitary body in the Plagiostomata, since the posterior part has an arrangement here, 
corresponding to that in those fishes. The communicating tube lies between the two 
lobes of the hypoaria, a position which is the same as that occupied by the sac in 
question in the Teleostei. If this is the case the saccus vasculosus in Plagiostomata 
is a new formation, and has no homologue in the osseous fishes. 
The haemal surface of the medulla oblongata presents a shallow, longitudinal, 
median furrow, the anterior prolongation of a similar one in the spinal cord, which is 
the representative of the anterior median fissure of the higher vertebrates. 
The cerebellum in Scyllium is cylindrical in its central part, but terminates anteriorly 
and posteriorly in pointed extremities ; its external surface is smooth, but presents in 
the midline a longitudinal furrow. 
In the Pays, also, there is a longitudinal furrow, and several subordinate furrows 
give the external surface a more complicated appearance. 
In Acanthias and Bhina the cerebellum is comparatively small, oval in shape, and 
is marked by a longitudinal furrow, which in the former is supplemented by another, 
placed transversely, forming the figure of a cross. 
At the sides the cerebellum is connected to the medulla oblongata by the crura ad 
medullam ; at the point of junction where these become the restiform bodies,'" and for 
some distance behind, some folds are developed in Scyllium, Acanthias, and Bhina. 
In the Bays these folds form quite a complicated arrangement. 
The medulla oblongata forms a wide shallow trough, the fourth ventricle, or sinus 
rhomboideus, which contracts gradually behind until it becomes merged in the spinal 
cord at the calamus scriptorius. In the Bays the fourth ventricle is much narrower than 
in the other species. The open dorsal part is covered by a process of pia mater, which 
is devoid of nervous tissue, but develops tortuous folds lined by columnar epithelium, 
enclosing both arteries and veins, and altogether has a glandular appearance. 
The spinal cord in Baja has a quadrangular section, its largest diameter being at 
the posterior end of medulla oblongata ; it gradually diminishes in size towards the 
posterior end of the body, and extends to within one inch from the extreme end of 
the tail. In specimens which I have dissected I did not find the enlargement at its 
anterior extremity as stated in Owen’s ‘ Anatomy of Vertebrates.In Scyllium, 
Bhina, and Acanthias, the shape of this part is oval, and slightly depressed on the 
* Busch, loc. cit., p. 23. | "Vol. 4, p. 271. 
