OF THE SKULL IN SHAfiKS AND SKATES. 215 



tinuously through the middle of the sense-capsules in the first figure, that will represent 

 the edge of the preparation figured in fig. 3. Such a line would bend strongly down- 

 wards (at about 120'^) in front of the ear ; and that is where the middle and hinder 

 regions meet; these are the trabecular and parachordal tracts. 



The parachordal tracts (i v), or investing mass, are cut away, as it were, to fit to the 

 convex edge of the ear-capsule ; and being bevelled, they pass under each sac somewhat. 

 They then broaden, where the postaural nerves (9, 10) pass out, and then, narrowing 

 a little again, are equal parallel bands, running without transverse segmentation some 

 distance into the cervical region ; and the numerous roots of the vagus and the following 

 spinal nerves are seen at their outer edge (fig. 3. 10, sjy.n). 



In front the parachordals thin out a little, and pass under the ends of the next pair 

 of bands — the trabeculse ; these are wider, shorter, and more solid tracts of crowded 

 cells, taking up the carmine more perfectly, and rapidly becoming hyaline cartilage. 



They form afterwards the flattest of skulls ; and now are wide flat bands, angular 

 behind, where they are wedged in between the parachordals and the ear-sac ; they then 

 narrow at their waist, and broaden into a rounded spatula in front, close behind the 

 olfactory capsules. 



They are not merely prcecliordal tracts ; for the notochord reaches to their middle 

 (PI. XXXV. flg. 3, PI. XL. fig. 7, tr, nc), where it is twisted, recurved, and constricted 

 in a moniliform manner, like the floral hairs of Tradescantia virginica. The rest of the 

 notochord is unconstricted, and passes, of an even size, into the uncleft spinal region. 

 The pituitary space is just equal in size to the notochordal tract of the trabeculse ; it is 

 oval, and is only finished in front by a newer and softer tract of tissue — the rudimentary 

 internasal band. The infundibulum passes obliquely into the pituitary sac {inf, py), the 

 latter getting somewhat under the apex of the notochord. 



Behind, the posterior clinoid edge of the trabeculse runs inwards and forwards and 

 externally ; the trabeculse then widen to their " elbow " or most projecting postero- 

 external point. In the angle between this point and the fore margin of the ear-sac, the 

 preeauditory nerves (5, 7) are seen as large leashes of young fibres in four main divi- 

 sions, the fourth (facial nerve, 7) hooking round the front of the capsule. Antero- 

 internally to that capsule a mass of cells can be seen, the rudiment of the Gasserian 

 "anwlion, and postero-intemally another smaller mass, the rudiment of the ganglion of 

 the ninth and tenth nerves. The oval olfactory sacs («a) have between them a dagger- 

 like internasal tract, which, like the covering of those sacs, is very soft at present ; this 

 is the rudiment of the internasal part of the trabeculse, the cornua, and the prsenasal 

 rostrum (i.nc). 



The pointed end of this tract now lies behind the mid brain, truly a remarkable posi- 

 tion for the rudiment of that long beak which afterwards forms the axis of the "cut- 

 water" of the Skate, and even of the Saw-fish, whose structure corresponds to that of 

 the Skate (Gegenbaur, pi. 14. fig. 2). 



2h 2 



