138 ZOOLOGY . SECT. 



portion of the skull are two small apertures situated n a mesial 

 depression. These are the openings of the aqueduet&s vestibuli 

 (endolymphatic ducts), leading into the vestibule of the membranous 

 labyrinth. Behind this again is the occipital region, forming the 

 posterior boundary of the cranial cavity, and having in the middle 

 a large rounded aperture the foramen magnum through which 

 the spinal cord contained in the neural canal and protected by the 

 neural arches of the vertebrae, becomes continuous with the brain, 

 lodged in the cranial cavity. On either side of this is an articular 

 surface the occipital condyle for articulation with the spinal 

 column. 



A number of smaller apertures, or foramina, chiefly for the 

 passage of nerves, perforate the wall of the skull. Behind and to 



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Wfe 



e.p.br.5 



FIG. 768. Chiloscy Ilium, lateral view of skull with visceral arches and anterior part of spinal 

 column ; the branchial rays are not represented. The skull and hyoid arch are somewhat 

 drawn downwards, so that the hyoid and first branchial arch are not exactly in their natural 

 relations. 6?-. 1 br.5 branchial arches ; cer. hy. cerato-hyal ; ep. br. epibranchials ; gl. aperture 

 for glosso-pharyngeal nerve ; b. hy. basi-hyal ; hy. mn. hyo-mandibular ; interc. intercalary 

 plates ; Mck. Meckel's cartilage ; neur. neural processes ; olf. olfactory capsule ; oc. foramen 

 for oculo-motor ; opt. optic foramen ; pal. q. palato-quadrate^ path, foramen for 4th nerve ; 

 ph. br. 1 first pharyngo-branclrtal ; ph. br.& fifth pharyngo-branchial ; sp. neural spines ; tr. 

 transverse processes and ribs ; tn.joramen for trigeminal nerve. 



the outer side of the anterior fontanelle is the aperture for the 

 ophthalmic branch of the fifth, or trigeminal, nerve. Piercing the 

 inner wall of the orbit are foramina through which the optic nerves,., 

 or second pair of cranial nerves (opt.): the oculo-motor (oc.), or third : 

 the pathetic, or fourth (path.) ; the trigeminal, or fifth; the abducent, 

 or sixth; and the facial, or seventh, gain an exit from the interior of 

 the cranial cavity. Just behind the auditory region is the foramen 

 for the glosso-pharyngeal, and in the posterior wall of the skull, near 

 the foramen magnum, is the foramen for the vagus. 



In close connection with the cranium are a number of car !ilages 



