536 WALTER EDWARD COLLINGE. 
Fie. 5.—Longitudinal section through a primitive pore from the opercular 
region of the head of Pol yodon. 
Lettering.—ep. Epithelial cells. x. 7. Nerve-fibres. p. Pit. sez. o. Sense- 
organs. 
Fic. 6.—Sensory organs from the lateral canal of Polyodon. 
Lettering—a. Modified cluster pore. 4. Sensory organ, unknown. ¢, 
Sensory organ, unknown, in group. d. Cluster pore undergoing division. 
Fie. 7.—Canal bones. 
Lettering.—a. Lateral view of the tooth-shaped bone in the anterior part 
of the rostrum of Acipenser, connecting the supra- and _ sub-orbital 
branches. x 8. &. The same, inner view. The apertures, a’, represent the 
passage of various branches, the 4 indicates the course of the main branch. 
x 8. ce. Dise-like bone from the lateral canal of Acipenser. x 5. @. 
Dise-like bone from the lateral canal of Acipenser; natural size. d. Canal 
bones from the head of Polyodon. x 2. e. Canal bones from the sub- 
orbital branch of Acipenser. X 2. 
Fic. 8.—Lateral view of the cranium of Polyodon, showing the exit of 
the cranial nerves. The opisthotic and pterotic are added from Bridge 
(16, pl. 55, fig. 3). 
Lettering.—a. w. Anterior nares. d. sph. Dermo-sphenotic. fy. g. Articular 
groove for the head of the hyomandibular. op. Opisthotic. ptr. Pterotic. 
The foramina for the exit of the cranial nerves are indicated by their respective 
numbers I to X. 
Fic. 9.—Copy of van Wijhe’s figure (82, pl. xv, fig. 4) of Polyodon, 
showing the relations of the cranial nerves to the hyomandibular, &c. 
Lettering as below. 
Fic. 10.—Corrected figure showing, in my opinion, the right position of 
the hyomandibular bone and cranial nerves, &c. 
Lettering.—c.h. Cerato-hyal. e¢. 4. Inter-hyal. 4.4. Hypo-hyal. 4. m. Hyo- 
mandibular. 7. Mandibulo-hyoidean ligament. /’. Quadrato-suspensorium 
ligament. Je. p. Ethmo-palatine ligament. J. Meckel’s cartilage. m. ad. 
Mandibular adductor muscle. pm. Outgrowth of masseter muscle. p. g. 
Palato-quadrate. g. Quadrate. 7. m. Ramus mandibularis, fascialis. 7. m’. 
Ramus mandibularis, fascialis internus. 7. m'’. Ramus mandibularis, fascialis 
externus. 7. m. 7% Ramus maxillaris inferior, trigemini. 7. m. s. Ramus 
buccalis. 7.0.p. Ramus opthalmicus profundus. +7. 0. s. Ramus opthalmicus 
superficialis. 7. o¢. Ramus oticus. sy. Symplectic. 
Fies. 1] and 12.—Diagrams illustrating the sensory canals of the head and 
part of the lateral canal of the trunk, and the nerves which innervate their 
sense-organs. The canals and branches are coloured yellow, the trigeminal 
nerve blue, and the facial red. The cranial nerves are numbered respectively 
Ito X. On the left-hand side the connection between the supra- and sub- 
