208 FISHES CHAP. 
vertebra, and between them the remains of the notochord are 
traceable into the cranial floor. In front of the occipital region 
two lateral bulgings indicate the periotic capsules, and more 
anteriorly still, in the trabecular region, the sides of the cranium 
are modified to form two spacious lateral recesses, the orbits, each of 
which is bounded above and below by supra-orbital and infra-orbital 
ridges respectively, behind by an outgrowth from the periotic 
capsule (post-orbital process), and in front by a similar projection 
from the hinder wall of the olfactory capsule (lateral ethmoidal 
Vu.5 aud.cp 
hed brat | Some 
Fic, 120.—Side view of the skull of the common Dog-Fish (Scyllium canicula). aul.ep, 
Auditory capsule ; 67.4 1, 5, branchial arches ; 67.7, br.r’, cartilaginous rays 
attached to the hyoid arch and the first four branchial arches ; Cr, cranium ; ea.br, 
extra-branchial cartilages ; hy.cn, cerato-hyal; hy.m, hyomandibular ; 7b, labial 
cartilages ; ly, ligaments passing from the jaws to the cranium and to the distal end 
of the hyomandibular ; dg’, ethmo-palatine ligament; 7.7, lower jaw or Meckel’s 
cartilage ; Nv. 2, optic foramen ; Vv. 5, foramen for the Vth and part of the VIIth 
cranial nerves ; olf.cp, olfactory capsule ; or, orbit; wp.j, upper jaw or palato- 
quadrate cartilage. (From Wiedersheim, after W. K. Parker.) 
process). In front of the cranial cavity and the orbits may be 
seen the laterally-placed dome-like olfactory capsules, which are 
open below, where the nasal sacs communicate with the exterior. 
Between the two capsules an anterior extension of the cranial 
floor forms a flattened mesethmoidal plate, behind which is the 
large, membrane-closed, anterior cranial fontanelle. The lateral 
walls of the cranium are perforated by numerous apertures, some 
of which serve for the entrance or exit of blood-vessels, and 
others, mostly pertaining to the inner walls of the orbits, for the 
transmission of the different cranial nerves from the brain to 
