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of the braincase form large lateral projections (auditory capsules) 

 containing the organs of hearing. 



At the center of the nearly vertical posterior surface of the 

 cranium is a large opening, the foramen magnum, through which 

 the spinal cord passes. 



At either side of and below the foramen magnum is a smooth 

 articulatory surface (occipital condyle) articulating with the cen- 

 trum of the first vertebra. 



The flattened ventral surface of the posterior part of the cranium 

 forms the roof of the mouth, or palate. 



In the mid-dorsal line of the cranium, between the prae-orbital 

 processes, is a small aperture opening into the brain cavity, the 

 epiphysial foramen. It is closed during life by a tough, fibrous 

 membrane. The stalk of the epiphysis extends to the under surface 

 of this membrane. 



Between the auditory capsules is a deep depression in the roof 

 of the cranium in the floor of which can be seen the two small 

 pores through which the ducti endolymphatici pass into the cap- 

 sules. Close behind them are two larger openings for the perilymph 

 ducts. 



A pair of foramina passes through the inner edge of the prae- 

 orbital process ; these permit the passage of the ophthalmic branches 

 of the trigeminal and facial nerves to the dorsal surface of the 

 snout. Near the bottom of the inner wall of the orbit is the foramen 

 of the optic nerve. In the postero-ventral angle of the orbit is the 

 large trigemino-facial foramen for the exit of branches of the 

 trigeminal and facial nerves; in front of it is the small oculo- 

 motor foramen. The extremely small foramen of the trochlear nerve 

 is almost directly above the optic foramen, near the top of the inner 

 wall of the orbit. Close below the trigemino-facial foramen is the 

 small passage for the abducens nerve. Below the abducens foramen 

 is the transbasal canal. Behind and below the trigemino-facial 

 foramen are two foramina, through which pass the hyomandibular 

 branches of the facial nerve. The foramen of the vagus nerve is 

 close to the foramen magnum, upon the posterior surface of the 

 cranium. The foramen of the glossopharyngeal nerve is lateral to 

 that of the vagus, near the postero-lateral angle of the cranium. 



The cranium of Eugaleus is much like that of Squalus, except that the 

 rostrum is formed by three rods, two dorsal and one ventral, which arise from 

 the front of the brain case and converge anteriorally until they meet and fuse. 

 The olfactory capsules are much larger and of heavier cartilage than in Squalus. 

 The auditory region similarly is more prominent. 



(2) The jaws. The jaws in reality are the first pair of visceral 

 or gill-arches, and in spite of the modification which has taken 

 place this relation can be seen easily in the adult shark. The 

 upper jaw consists of a pair of palato-quadrate cartilages, united 

 medially by ligament, and bearing the upper series of teeth. A 

 large hooked palatine process extends from each palato-quadrate 

 cartilage upward along the inner wall of the orbit. The lower jaw 

 likewise consists of a pair of MeckeVs cartilages, united medially 

 (the union is called the symphysis), and bearing the lower series 

 of teeth. A pair of small labial cartilages, which support the edges 

 of the labial pockets, lie at each corner of the mouth. 



(3) Visceral arches. The first of the visceral arches is much 

 larger and heavier than the rest. It is known as the hyoid arch. 

 Each side of the arch consists of two rods of cartilage: (1) the 

 hyomandibular cartilage, which articulates with a distinct facet on 

 the lateral surface of the auditory capsule, and extends from here 



