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 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 {209}various parts of the head. In many Elasmobranchs the roots of certain of the anterior spinal nerves perforate the side-walls of the occipital region, and indicate the fusion of vertebral components with the cranium. In the cranial roof between the two periotic capsules there are two small apertures at the bottom of a common median depression: through each aperture the ductus endolymphaticus (_aqueductus vestibuli_) passes from the vestibular part of the auditory organ to the exterior of the skull. Three cartilaginous rods, one from the roof of each olfactory capsule, and one, the _prenasal_ or _rostral_ process, from the ethmoid cartilage, converge and meet, or nearly meet, in front to form the rostrum or support for the preoral or "cut-water" portion of the head.